Like PENG and many others here, I have used a separate amp, but found no real improvement. I have my volume set to run from -80dB to +18dB. Very rarely do I set the volume above -20dB (and when I do, it is because it is a quiet recording, so that hardly counts). I set the AVR to not go past -10dB once I established that I would never listen that loud as a protection against a toddler wandering over and grabbing the volume knob (or my brother who sometimes drinks a bit too much and loses his senses
![Smile :) :)](data:image/gif;base64,R0lGODlhAQABAIAAAAAAAP///yH5BAEAAAAALAAAAAABAAEAAAIBRAA7)
).
My point is I feel very comfortable that I am not pushing the limits of my AVR and ended up removing the separate amp from the system (I'll sell you a gently used XPA-2 for $475 plus shipping!). So definitely try the AVR on it's own first.
On the topic of power and adequate headroom, if you get a good sub and cross it at 100Hz (the FR for your speakers puts the bottom end at 70Hz), you will be freeing up even more capacity of the AVR's amp section by letting the sub take on the power-heavy demands of bass!
In case it is not clear, along with Mark, I believe you should shift from buying AVR and amp to buying AVR and sub. You can always add an amp later if you need it, but I believe a good AVR and sub will get you "more better, more sooner"!