That's wierd. I would be careful about drawing any conclusions from this. The subwoofer output is the only place where a bigger/better receiver should NOT make a difference.

Did you have a chance to check the channel levels between the two receivers ? It sounds as if the sub level might have been turned down relative to the other speakers on the 235.

M60ti, VP180, QS8, M2ti, EP500, PC-Plus 20-39
M5HP, M40ti, Sierra-1
LFR1100 active, ADA1500-4 and -8