The P363/PC351 are very good bang for the buck speakers for medium to large rooms but if your room is large enough to justify those speakers then it's screaming for a bigger sub. I can't really recommend anything without knowing the total volume of the room including any attached spaces that are open to the room. I'd take some measurement and then contact
Hsu Research and
Outlaw Audio and have them recommend something capable of really filling that room. If you can't swing a large enough sub right now then I'd do without while you save up. Those speakers play low enough that you can get buy just fine without a sub while you save up and do it right.
A Denon AVR-2113 would be a good choice for a receiver or a 3312 or 3313 may be a be a bit better. I've had good luck with factory refurbished receivers from
A4L but if you shop well or catch a sale you may be able to find new or open box for almost the same price.