I'm looking for a used 5 channel amp

My problem is limited shelf depth. The shelf is only 16 inches deep. 50 watts a channel should be enough to drive my Cambridge Soundworks front speakers and Klipsh in ceiling rears. I suspect my Onkyo receiver (50 watt) isn't strong enough and hope to get better sound with components. Any suggestions are welcome. I've never owned anything but mass market gear and am not very knowledgeable.
Are you looking for an power amp or an all in one receiver/amp receiver. If you are looking for an amp only, then investigate a brand called ATI. The ATI 3 channel amps are not very deep. Look up the ATI 1505 which is 150 watts, 5 channels. Don't be put off by the power ratings
I think you can get a Parasound 855 for around $400. It has 85w/ch and will make a nice upgrade. If your budget is set higher, then there are many.
Thanks for the quick reply! I'll look at the ATI and Parasound. I thought the Carver AV 505 would be good, but it is 17" deep. Somec59, forgive my ignorance, but what do you mean when you wrote "don't be put off by power ratings"?