If using only Serial connection, any radio that emulates the SL30 protocol serial output, such as MGL's upcoming Nav radio. I think XCom does this too, not sure.
If you have the HS34, which I believe you plan on, then just about any Nav radio that outputs ARINC 429.
The HS34 is definitely part of the plan. Is there a listing of radios that output over ARINC? I would assume a KX 170 does not but what about the KX 155/165 series? Any of the Narco or Terra stuff?
You are too modest. You also know that the Garmin (Apollo) GNS 480 works fine, both in serial mode (non-precision GPS only, should be identical to SL30 for Nav) and ARINC (precision GPS and ILS).
By the way Dynon - I really would like to recommend that you update your compatibility matrix on the Wiki to include both GPS and Nav, and to differentiate between compatibility for legacy units, HS34, and SkyView. That would make it a lot easier for folks to quickly check compatibility and required "extras" for a particular unit.