The snow installer has no "options" button, and no way to explicitly ask for an archive & install. But the outcome is a little more unexpected. The installer boots, and when you try to select the volume, it says you cannot start from OS X from that volume. It's like what happens when you try to install onto a APS partitioned volume. It's saying you need to reformat. (somewhat OT but related, intels can start fine off APS formatted volumes, all my service drives are formatted that way because PPC cannot start off GPT, the only snag is 1. the OS installers lie and say you can't use it, and 2. the firmware updaters refuse to run)
Since a PPC can't boot into Snow Leopard anyway, there's no reason to continue hanging onto APM, and lots of reasons to move on to the superior GPT on your new iMacs. (For one thing, APM cannot handle a drive (not a partition) larger than 2TB without changing sector size to something larger than 512 bytes. Changing the sector size confuses some third-party disk utilities, so Apple provides no way to do it.)
Besides, the ability to boot an Intel machine from APM is a feature supported by the firmware in the machine. New machines may well drop that support. Machines that ship with Lion, in particular, have support for the Recover HD partition and for Internet Recovery (both accessed from the new Command-R startup key combination). It should not be unexpected that new firmware will someday drop the ability to boot from APM. Past performance is no guarantee of future results.
If the new machine came with Snow Leopard or earlier, it's easy to go back. Just restore from backup. (You do have backups, right? That's the only way you could have put Snow Leopard on an APM disk in the first place. As you've (re)discovered, the installer cannot be coaxed into doing it, and the old trick of installing on a PPC machine won't work either.)
A new machine that came with Lion installed can't run Snow Leopard anyway.
1) get your time machine backup current, erase and install 10.6, and restore from backup (I am concerned that 10.6 may not want to restore from a 10.7 time machine backup - anyone tried it yet? or are you hosed it time machine got a backup ran after you upgraded?)
This was actually one of the first things I tested with Lion. (Time Machine fascinates me.) I had an extra 1TB drive laying around, so while still under 10.6.8 I formatted it into three partitions:
- I cloned my TM backup to one partition, and used SuperDuper to clone InstallESD.dmg on top of that (using SD, because it will leave TM unharmed if it finds it on the destination volume of a clone) so that that TM partition was now also a Lion Install Disk.
- Onto the second partition I cloned my Snow Leopard boot volume, using SuperDuper.
- The third partition I left empty.
Then I installed Lion on my main system, and let TM take a few more snapshots of that to the TM clone on the first partition.
Then I tested the Lion Install Disk I had made of the TM partition, trying every combination I could think of. It successfully:
- Upgraded the SL clone on partition 2 to Lion
- Installed Lion on the blank partition 3
- Restored partition 2 back to SL from the TM backup on partition 1.
- Restored partition 2 back to Lion, again using the TM backup on partition 1.
- Erased each of partitions 2 and 3 using Disk Utility, both the DU on the Lion Install Disk and the normal one on my main Lion partition.
- ...and many other tests, including repeating some of those tests using the Restore HD partition and the Lion Install Disc I had burned onto a DVD.
The only hiccup I ran into was that every time TM restores a volume, it wants to rename that volume the same as the volume it backed up. That always left me with two volumes with the same name. The OS isn't confused, because all disks were GPT so volume names are unimportant, but I was afraid I would be, so I had to manually change the name back after each TM restore.
Don't forget that the TM backup itself is OS-version agnostic. All the smarts in TM go into creating the backup, but the backup itself is dead-simple boring. If a TM backup contains snapshots from both Snow Leopard and Lion, you can use TM in restore-whole-volume mode to go back to one of the SL snapshots, and then use it in normal mode to restore the documents you changed while you were running Lion. Restoring from an old snapshot does not preclude doing additional restores from newer snapshots.
Also, you said "erase and install 10.6, and restore from backup". You don't need to install 10.6 first, nor even erase the disk. Just restore the whole disk, while booted from any install disk (including Lion's Recovery HD), and you'll get whatever OS was backed up to that snapshot. If you use any of the Lion restore mechanisms, and restore to non-Lion, the Recovery HD partition that was carved out of that volume gets re-absorbed. (Actually, Lion does this any time it erases a volume followed by a Recovery HD volume. If you then restore or install Lion onto that partition, the Recover HD partition gets carved out anew.)
2) perform some other form of backup. erase and install 10.6. Manually restore applications and user accounts (I'm favoring this option)
That'll work, but TM restores are smooth and fast. Select a SL snapshot to restore from, start it going, and go grab some coffee. When it's done, so are you.
3) purchase an external hard drive and install 10.6 on that and use it when needed (was recommended to above customer)
That also will work. I'm doing the moral equivalent: I kept my SL machine around (I only bought a new iMac because the old one won't support Lion) and keep using Quicken on that.
Bear in mind that there is always a cost to booting back and forth between versions of the OS. They often don't trust each other, and will rebuild files that they don't think the other one kept up to date. OS X would always force MacOS 9 to rebuild its desktop database, because OS X couldn't be bothered to maintain it; Tiger would re-index its Spotlight database if it saw that an earlier version of the OS had touched the volume. (Snow) Leopard throws away its FSEvent log if it sees that an earlier version used the volume, forcing your first TM backup after coming back to require a time-consuming deep scan.
Lion is no different. Lion and Snow Leopard apparently don't trust each other's Spotlight databases, because I saw Spotlight re-indexing all volumes every time I switched in either direction. (This observation was a side-effect of the TM+Lion Install Disk testing I mentioned earlier.) Fortunately, re-indexing is a lot faster than it used to be.
So... if you go to Lion, you'd better be sure you're going to like it, or make darn sure you have your ducks in a row for reverting, and prepare for the headache.
I had all my ducks in a row, did lots of preparation and testing, and in the end discovered that I really like Lion. It's a big change from Snow Leopard, and it took about a week of use before it became comfortable, but I'm now satisfied that the change was very much for the better.
The trick, as always, is: don't fight the new system. Don't rush to reconfigure Lion to behave just like SL, or L, or Tiger, or MacOS 9, or whatever you were last comfortable with. Leave the default scrolling set the Lion way. Learn to like Xcode 4.1. Turn on all the multi-touch gestures. Use them.
Everything feels strange at first, but it doesn't take long to get used to it. There's a brief disorientation when you go back to a SL machine, but it passes quickly. It's just like the disorientation when moving between SL and Tiger and their different Dock behaviors, or the disorientation going back and forth between an automatic transmission and a stick shift. Each time you do it, the transition becomes easier, and eventually you don't even notice that your left foot seems to just know whether it needs to work a clutch or not, without you having to think about it.