All I can say is that I'd really recommend a separate amp, especially in your case.
Whatever the manufacturers say, a HU will only put out a realistic 15-20w per channel rms/continuous (peak power is an irrelevant measure that is used primarily for marketing).
An separate amp will dramatically improve sound at all volume levels over even the best HU internal amp.
Get a basic HU with the minimum of features you want, but make sure it has got dual pre-outs. Then, spend about $150 on a decent 4ch amp. Something like a US Acoustics USX-4065 (65x4 for $150) would be perfect.
Go out and audition different speaks to find out which ones sound best to you.
Hook it all up, and you'll be very satisfied. And we're talking of a system around $500 (HU-$250, amp-$150, 4speaks-$150)
