Receiver vs Separate Pre and Amp

I want to know what's the advantage of a preamp + Amp setup vs using a receiver?

I had a Rotel RSP 1572 with a Parasound A51 + A52 setup before. However, now I have a bigger house so I moved the Rotel and A51 upstairs with a pair of electrostatics mainly for music. The down stairs unit is now composed of a NAD T757 V2 and the Parasound A52 mainly for movies.

Obviously, you are going to notice that the down stairs 7.1 setup is now a major downgrade since a pre-amp is now replaced with a receiver. The question now is, what is the advantage of the pre and amp setup versus the receiver?

FYI, I am only using the receiver to drive a pair of subs + the surround backs. The Parasound halo A52 is hooked up with the pre-outs on the receiver to drive front, center and the surrounds. An active sub is also used with the sub pre out. I read somewhere that people use separates only because separates can deliver higher power whereas receivers rarely pass the 100 watt mark. Is that the only difference?

Thanks!