Does the UMC-1 have bass/treble settings? If so turn the bass up a notch or 2 to see if that helps with the lower volume play back. I like Audyssey just for this reason, it boosts the bass and treble for lower volume playback and it works very well.

Jason
M80 v2
VP160 v3
QS8 v2
PB13 Ultra
Denon 3808
Samsung 85" Q70