Here are the steps I would go through to isolate the cause of the VP160 sounding thin:
Disable all auto EQ functions and tone controls in the Denon. Set the fronts to large and set the sub to "No". Disconnect your right front M60. Put the Denon in pure direct mode. Put on a stereo recording and listen to the left M60 only. Make some notes on the sound, perceived bass, full or thin, etc. Now swap the left channel cable to the VP160, without moving the centre from it's correct position. Play the tracks again and compare your notes. If the VP160 sounds thin in comparison then it's either an issue with the speaker or the room/placement. If it sounds OK you now know it has something to do with the receiver set up. I always do a manual setup, which is time consuming but far more accurate than any auto EQ because your ears are involved! If you want to play with Audyssey after you have the system dialed in properly, go for it!
