Having only experience with the RX-V2500 as a pre/pro using external amplification, I can't give you much feedback on the NAD. However, knowing how impressive the pre/pro section of the 2500 is (my thoughts as well as serveral others here at AH), your comments about your music/HT listening ratio and that you could pick up a good 5/7 channel amp for less than a grand, I really can't see the NAD performing any better than the Yamaha with outboard amplification.
In my setup alone, it's cost me less than $1500 to run two separate amps (200w x 5, 100w x2) along with the 2500, which I believe you may be hard pressed to get better results... -TD