Amp recommendation in the $6000 range

I'm surprised the 500 watt Rowland M312 would lack bass compared to the XA100.5, I guess we're comparing stereo to monoblocks. I had a X250.5 years ago and it sounded great which is why I'm considering Pass Labs again.
What's the difference between the later X350.5 compared to earlier, the specs haven't changed.
Thanks for the input guys, I'm researching each amp you've recommended. 

Yeah those VTL caught my attention as well, it's one I'll put on my list.

Been hearing mixed reaction from the new Pass .8 series, I know the  X250.8 did really well at the recent EXPONA according to TAS.

jl35 - can you share the difference between X250.5 and X250.8, positive and negative please?

Thanks for pointing that out Al, I will take that into consideration.
As mentioned previously I've had the X250.5 before and liked the synergy which is why I'm wondering X350.5. 

I still have the Eklipse preamp and much of my system remains the same, what's different is I now have a dedicated room and will update the pics in my system in the near future.
A member here PM and alerted me to the D'Agostino Classic stereo, I decided to pull the trigger on it unseen in the flesh and unheard. There's a review on it in the newest TAS and a few who's heard it says it is very good, smooth, detailed, and not sterile. It is a 300 watt stereo amp with core technologies based on the D'Agostino Momentum but in a larger chassis, it also has input impedance of 100k ohm which should match more preamps. I imagine this amp to be some what similar to either the Pass Labs X or XA amplifiers.

Al, the D'Agostino doesn't provide RCA input but does provide XLR-RCA adapters with their amp, if they offer this, I would expect it to work flawlessly with an unbalanced signal. I have a feeling even though the connector on the back is an XLR, it is in fact unbalanced.

Same goes for the Eklipse preamp, it has XLR output, but the signal is unbalanced.