In their apparent effort to be very precise the Audacity instructions actually seem to have made a simple straightforward drag and drop install unnecessarily complicated….

There are four downloads offered on the Audacity download page
  1. Audacity 2.1.2 .dmg file (includes help files)
  2. Audacity 2.1.2 .zip file no help files
  3. Audacity 2.1.1 screen reader .dmg includes help files
  4. Audacity 2.1.1 screen-reader .zip no help files
Apparently the assumption is you chose number 1 the Audacity 2.1.2 .dmg file which would have been downloaded to your download folder and depending on your settings in Safari it may have opened automatically on your desktop or you may have to double click the .dmg file to open it. In either case a /Volumes/Audacity window opens which contains a folder labeled Audacity and an icon labeled Applications with a curved arrow pointing from one to the other. I just tested on my computer running Sierra (which has much tighter security than OS X 10.6) and had no problem dragging the Audacity folder to the Applications icon in that window, which copied the Audacity folder to the /Applications folder on my boot drive. Then at the extreme bottom left of the /Volumes/Audacity window there you will see 💻 Audacity 2.1.2 > 📁. Control+Click on 💻and select Eject Audacity 2.1.2 from the context menu that appears.

I don't think you will encounter this in OS X 10.6. but in Sierra when I attempted to launch Audacity 2.1.2 I received a message that Audacity is from an unknown developer and cannot be opened. I immediately went to System Preferences âž­ Security & Privacy, clicked on the padlock icon and entered my administrative password, found the message "Audacity.app" was blocked from opening because it is not from an identified developer and clicked on Open Anyway.

Since I have no way to replicate your unique situation I can only guess at why you are not able to hear the playback as you are recording but the first place I would look is Audacity ➭ Preferences ➭ Devices ➭ Playback and see what device is selected. Does that correspond to System Preferences ➭ Sound ➭ Output? What is the output volume setting? By any chance is Mute checked (✓)?

Audacity appears to be a pretty robust app and since I installed it looking for an answer to your problem, I think I will keep it around for a while at least. Thanks for the idea.

If we knew what it was we were doing, it wouldn't be called research, would it?

— Albert Einstein