PS Engineering intercoms are fantastic. They have separate amp circuits for pilot and copilot so you don't have such issues with mis-matched headsets. They are not cheap, but you get what you pay for. We run a PM3000 stereo unit in the RV-8 and I also had one in my old Cherokee. It outclasses the cheap Flightcom 403 by a huge margin IMHO. The music input with "karaoke mode" on the PM3000 is the best I've ever experienced on an aviation intercom. I had a Flightcom 403 in the Cherokee for a while and the PM3000 was a very worthwhile upgrade for me.
I can back this up. I have mismatched headsets as well, Bose X and Nordicas. The plane had a Flightcom 403 when I bought it, and I could never find the magic squelch spot to make cockpit conversation comfortable. No problem with levels, just squelch. The Flightcom also opens both microphones when either headset breaks squelch, so when anyone is talking, there is twice as much background noise as there needs to be.
I upgraded the Flightcom to a PS3000, and the difference is amazing, my wife even noticed immediately. Now we can have comfortable conversation without constant fiddling. The PS3000 only opens the microphone that actually broke squelch, which increases intelligibility drastically.
Also... I'd wired in music inputs to the intercom, and my ipod nano sounded horrible through the flightcom. There were clearly gain staging issues, at decent levels the music clipped pretty obnoxiously. Low end response was nonexistent, completely rolled off, and high end not much better. In contrast, the PS3000 sounds immaculate... plenty of gain, actual low end content, clarity on top, no clipping.... it's night and day.
Both the Flightcom and the PS3000 use 25pin dsub cables, so rather than dive into a full intercom rewire, I just made up a short adapter cable. Works fine, and it let me very quickly switch intercoms to A/B compare.
-jon
