That Onkyo will drive the Primus just fine especially, since you are just doing 2.1 for now. I had a $100 Sony receiver drive my P362B's without issue. I couldn't imagine the P162's requiring more power, as they're bookshelves.
FTR, I think you should audition all 3 especially the Boston Acoustics. Are you considering any of the Internet brands (AV123, Axiom, SVS, Dayton, Elemental Designs, etc.)? Floorstanders and subs really push up the cost of shipping for Internet stuff, but bookshelves (and in-walls) are relatively inexpensive to ship.
$500 for a receiver puts the Harman Kardon AVR-254 into contention as well. I would definitely look at something from Yamaha or last year's Denon's, too. I don't think you'll get a Pioneer Elite, Marantz, NAD, Rotel or Cambridge Audio for that money, but I bet you can find a (non-elite) Pioneer.
You mentioned movies and music. What about Blu-Ray/HD DVD? If you don't need HDMI or high res-audio, your options go up tremendously.