A few folks have gone to the trouble of using the preamp outs on their new HU's. 99%, like me, just used the speaker level outs. My Pioneer is 17 WRMS as I recall and it just sounds great. A bit louder but not excessive.
I installed 4 ohm Infinity 6.5" 2 ways in the doors and once again-great.

And if you do go with the pre-outs remember that they are RCA coax connector. You'll have to make adaptor cables.