Our first flight with the Garmin GFC 600. Today we flew our BE 55 for the first with the Garmin GFC 600 installed. Our panel include the Aspen 1000 Pro, GTN 650 and the GFC 600. Have to admit we are a little disappointed with the Aspen/GFC 600 Compatibility. I have a total Garmin stack, the Aspen 1000 is the only non- Garmin piece of avionics equipment in the aircraft. The disappointment arises with the inability of the GFC 600 A/P to capture any Altitude preset (Climb or Desc)/ VNAV/ Constraints. This was not made abundantly clear through the purchase process while speaking directly to Garmin Reps. The problem has been explained as a compatibility issue between The Garmin GFC600 and Aspen 1000 yet the STC authorization was issued. Have been told the issue is in the works but no timeline established. From what the avionics shop has informed me, this is quite possibly the first BE-55 instal of the new GFC 600 if not the first GFC 600 install on any Beech aircraft. Overall, a nice A/P however, one of the most important safety features of any A/P is the ability to protect and honor Altitude presets--the new GFC 600 DOES NOT with the Aspen 1000...yet! Stay tuned, more flight testing in progress.