DISCUSSION WITH APPLECARE
I was just on the phone with AppleCare for 1 hr and 3 min; up to the AppleCare senior Advisor level. I clarified with them several times what I am about to tell you now, informing the advisors that I planned to report what they said to this board.
In short, Apple outright stated, as far as they can tell, that a Mac is NOT equipped to allow a Logitech wireless/bluetooth headset nor a direct-USD Rosetta Stone headset to play a mic through the headset. (Their marketing department should love that one.)
I made the remark that the Logitech H800 headset did, in fact, play through the headset for a day! —but never after I rebooted after that first time. I was continuously nudged, of course, to the idea that is was the headsets fault, but the fact that the Mac did play “thru” once-upon-a-time somewhat nullifies that argument. Also, the headsets do NOT require their own software, which eliminates “driver-type” issues. (I will give AppleCare credit in that they didn’t waste an hour having me re-preform all the obvious ‘System > Volume’ and ‘Midi Audio Device’ gyrations; and they did, with only a little prodding, move the case up the support ladder.)
I told the advisors that the 3rd party program “LineIn.app” DOES allow the mic to play thru the headset, but it does so with an echo. And speaking of play thru, I pointed out the fact that the MIDI controls do come with a “Thru” option, but that the option is grayed-out, seems like the culprit. My suspicion is that if I could just click on the MIDI ‘thru’ button, the mac would do for itself what LineIn.app tries to accomplish. I'm sure the "thru" option was not placed there for good looks.
Here’s where it stands. I have a case number, and AppleCare is checking with their hackers to see if some (my words, no theirs) switch has been changed from TRUE to FALSE, or from ON to OFF somewhere in the software preferences. And the electronic switch has caused the "Thru" option to become grayed.
For those of you interested, I will advise on how things develop from here.