Receiver for pre/pro?

I've currently got a NAD T752 receiver and am looking at an outboard amp as an upgrade. I'm 80% 2 channel music but do use the system for 5.1 surround sound with movies too.

Thinking about an amp from Pass Labs either the X150 (2 channel) or X3 (3 channel to include center channel).

Looking for opinions from people who use or have used a receiver as a pre/pro and an outboard amp. Does music sound much better with this setup as opposed to using the amp in the receiver? Volume isn't a concern for me as the NAD is plenty loud enough.
One more question on this subject. If you take a rather warm sounding receiver like NAD or H/K and match it with a brighter amp like a Adcom or maybe Acurus-Aragon, will amp's sound take over and you lose the warmth?
Well in my opinion--you wouldn't do this unless you had an amp you knew was much better,--in the first place. If you're just experimenting with something you already have,that is one thing.---I do again want to state the importance of the center speaker/ amp quality.There are so many less than stellar center speakers out there.
The reason I asked was that I have a 50 watts into multi channel H/K 230 and would like to boost at least the front three channels to about 80-125 watts. Maybe a used B&K. But if the H/K's warm sound wouldnt dramaticly change, something like the Acurus three channel amp that resells for a decent price used looks promising.
I have an very nice Ohm Acoustics center channel so I have that base covered.
I'm currently using a Rotel 1055 receiver as a pre/pro with Parasound Halo outboard amps. This is a stop-gap set-up while I finalize my pre/pro options. For HT, I noticed more dynamic and focused sound. Tighter bass and an overall more enveloping experience. For 2-channel the difference was even more pronounced with a clarity and soundstaging which brought new life to music.
Jer, it is pretty hard to have a warm-sounding receiver without a warm-sounding power amp section. Pre-amps tend to be more neutral than power amps. So, if you bypass the power amp section, it is a crap shoot as to what the tonal quality of the pre-amp section is. My bet is it would be more neutral than the receiver as a whole. Adding a bright-sounding power amp will probably result in an overall bright sound.

My recommendation is to get as neutral-sounding of a power amp as possible. You will probably own it longer than the receiver and a neutral amp will always be the easiest to integrate into another system.