Luxman M900u stereo vs Mono setup

I'd be interested to hear someone's comparison, too.  I run TAD CR-1's, and recently acquired an M900u to try with them in place of the PS Audio BHK 300 mono's that I have been using.  The stereo Luxman amp is bringing some clear virtues in the mids and highs in terms of revealing musical and harmonic information, and that is appealing; but I find that I am not as happy with its low-mid bass, where it seems less distinct, almost feeling a bit vague.  This surprises me, given the 700+ damping factor that the Luxman boasts - - I would have expected greater control and definition, and I am hearing the opposite.
Yes, the stereo Luxman seem able to play loud enough in my 22.5' x 15' x 8' room.  But the bass quality in the match to my speakers could be better, I'm feeling.

So, if going to mono blocks would improve this bass issue, then I would have to consider if I can go that far in budget!  I hope someone has direct experience that can speak to this aspect.

I certainly agree that a 4 ohm load shouldn't cause a difficulty for the Luxman amp, in theory, and that is part of the puzzle.  I have not moved speakers even a mm, just subbed in the Luxman for the BHK mono amps and I hear this difference in bass.  My room is extensively treated, including bass traps.  I use high quality cabling throughout, cables that have made every other component they've been hooked up to sound excellent.  But it just might be that this needs some sorting to get the best of the Luxman. 

I will try some speaker placement work to see if there is a new "best spot" given the change.  It would be delightful if that ameliorated the issue, because the rest of the spectrum has a lot of plusses.  I sure wasn't expecting a bass quality issue....

Hmmm....   I would not fault the Luxman for transient impact and precision, IME.  They seem to bring out all of the startle from my beryllium mid/tweets.  That's part of their attraction, I find.

@hiendmmoe   Where have you heard that comparison between stereo and mono?  I would love to read such an evaluation.  Thanks!