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.
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.
Forget the receiver as a pre/pro! It's still not as dynamic (nor usually as resolved) as a dedicated pre/pro! Receivers are usually softer in the dynamics department.
But, yes, amps in receivers really blow! You'd do better outboard amp-wise..and better, yet again, using outboard pre and amp.
I just added a Sherbourn 5/1500A to my Sony DA4ES receiver. The sound is clearly tighter and more controlled, but not as big a difference in the bass as I had expected. And as Flrnlamb has said, the dynamics are not that much improved. I have yet to really crank it up on a movie yet, so I may see a bigger difference then.

I do need to investigate just how good the interconnects are that I just got to hook the amp to the reciever. They are Belden 1505F from Blue Jeans Cable.