Update: Went and spent an hour with my 12 year old daughter keeping notes of our "experiments".
GREAT NEWS: got the intercom, all the various headsets,and comm 1 (the old Garmin GPS300) working crystal clear. Better than I've ever heard them. Did a radio check from inside the hangar to ground and we were having perfect, old school landline quality voice communications.
Other news: comm 2 (Terra 760D) is dead. I pulled the breaker on it and everything else in the panel is perfect.
So, either put a yellow tag one in of the exact same radio (around $500-$1000) and fly on, or use this chance to pull it and the TN200 VOR (they are installed as a pair in a weird bracket) and put in a GNC215 (about $4,700 plus unknown amount to install).
Good news that we're not grounded anymore, as comm 1 is crystal clear now and there are no anomalies. Comm 2 is disabled and placarded as INOP until I get either a replacement unit or upgrade.
Germain to this, do we really even need VORs anymore or would I be fine to just put a GTR205 for like $2700 and remove both Terra radio nav/coms?
I think the smartest short term thing is to slide a working 760D in, but it's throw away money when I eventually upgrade other components.