too warm?

that depends on what you like.

being that the Aperions are slightly warm at most, and the Pioneer Elite receivers are also slightly warm I doubt you'd end up with an overly warm (midbassy) sound.

personally, I tend to prefer a little warmth which is why I intend to pick up one of these receivers soon. of all the receivers I have auditioned, the Elites were the most impressive. I compared them to Rotel, Denon, and Yamaha.

I have no idea about Onkyo, but I can say that I have always been unimpressed with Denon's sound. even still, Denon makes some nice gear.