Let's start with...where are you? As in, what headphones do you currently have? How's it working out of your Pioneer? How good's your hearing?
EDIT: That was written before you posted what you have.
If you don't have anything less than freebie earbuds, you might want to start smaller, like Sony MDR-7506/-V6, and take it from there. The reason I pick those is that they're already pretty sensitive, so should be driven well by your Pioneer, have plenty good bass, and are decently comfortable (more so than Grados, anyway). They can sound a little bright (not sibilance bright, but if there's any sibilance anywhere else in your chain, it'll be enhanced...more like just a lot of emphasized upper frequencies bright -- it'll also force you to listen at more reasonable volumes), but you can get used to that -- even addicted. And if you're older and deafer, it might even compensate for those frequencies being attenuated.
EDIT: The above recommendation remains. I don't think HD650 would work well out of a receiver.