Musician vs. audiophile

Odd that the OP has not chimed in again at all
What started out as a fairly interesting technical thread with some great posts seems to have devolved into more one of semantics and opinions, not that there is anything wrong with that of course.
OP may be genuinely busy as it that time of year.
Does remind me though of throwing a bone out and letting the dogs fight over it.........

I would like the op to chime back in if possible with a bit more information like type and model of source, are the room sizes and types of the 2 different systems remotely comparable etc etc.

Exactly Charles.
Indeed one of the members here might listen to the ops rig and not hear "flat" at all!
However deep down the only opinion of how it sounds that counts is the ops( and his good lady of course) so if flat and uninvolved to them then a fix is to be found.

You did not state what power amp? Assuming it is a BAT too but who knows.
Now I must state from personal experience and a number of other comments I have read that BAT and Wilson speakers are usually a marriage made in heaven IF everything else is correct. I have no experience of the BAT preamp but I use a BAT power amp to drive my Wilson's and I am wanting for nothing. Imaging and soundstage are superlative and bass response can cause bowel movements....lol.
Even at low levels for evening duty I am losing nothing and flat is not a word I could ever use.
Als suggestion to disconnect the subs is excellent and the first place to start. 
You also have no mention of source? Streaming, CD,vinyl?? Could be numerous issues there too.