Zd, that looks like what he has, and according to the company website this unit can drive "traditional speakers", however his speakers may not be tube friendly due to their impedance/phase angle relationship.
Is the impedance switch on the back of the amp set to 4 or 8 ohms? Sometimes 8 ohm speakers with an impedance that drops severely at certain frequencies will sound better on the 4 ohm tap of a tube amp. Have you tried both switch positions? And switch only with unit powered off.
Also, here is something you may try with the Pioneer.
Connect to video, then in the menu for 5.1 adjustments, set front L&R to "large", then center, surround, and sub to "none". Now use front L&R out instead of the 2ch L&R out.