It depends on the size of your listening room; if you tried the receiver in a very large area (greater than 3000 cubic feet) you'll need a lot of power to generate adecuate levels of sound pressure, on the other hand, the computer speakers generally are "in your face" and if you're in your bedroom the effect is maximized, that's why you hear them louder. Or maybe your receiver do has a fault. I have a RXV1400 in a less than 1500 cubic feet listening room with moderately efficient (91db) speakers and it sounds pretty loud at -15 db.
Another thing, these receivers a particularly complicated to use, you'll need to read the manual like 5 times and a few weeks of tweaking to get the full potential of your system.