For some time, my intercom has been malfunctioning when both headsets are connected in the plane. The headsets distort badly. This is not a radio issue - the radio works fine (otherwise I would probably have been forced to land by the authorities).
The original intercom in the plane is a mono intercom built from a kit at the same time the plane was built. I have been wanting to install a stereo intercom for some time. However, the main replacement issue is that the intercom is currently installed in the panel on the right hand side of the plane in the front seat area where the fuses and switches are installed. The current intercom is on a circuit board that measures only 3 inches long by less than 2 inches wide, so any replacement intercom would need to be able to fit into the same space. I have no current panel space for a conventional panel-mounted intercom.
After some searching, I finally located a suitable intercom - the FlightTech ITC-402P. It comes as a kit for panel mounting, but the board can easily be removed from the kit and installed in the same slot as the current mono intercom. I ordered it from Spruce for $269.95. Initially I suffered from finger trouble and ordered the wrong darned version - they sent me the 2-place portable version of the intercom. I sent that back for credit and re-ordered the correct item.
The headphone speaker jacks will need to be rewired for stereo also. No big deal. I bought the wire and jacks for this from B&C.
The circuit board for the intercom is tiny. Here it is:

This should easily fit where the current mono intercom board fits.
The intercom has automatic squelch, ENRI noise reduction, pilot and co-pilot PTT, aux stereo input with automatic mute (this will be even better when I connect up my XM Radio circuit - I dream of a Garmin 396 for next Christmas) and pilot isolate.
My only complaint is that the Installation Guide is close to unreadable, because they printed it as 2-ups on 8.5 by 11 paper to save space. The lettering is way too small, and the printing is not firm enough. When I scanned the pages at 150 dpi, I found the manual to be much easier to read. I will be printing it as single pages on 8.5 x 11 paper to make life easier.