Denon/Marantz/Onkyo receiver will be no match in 2-channel for a separate pre-amp in the vast majority of cases. I built a separate 2-channel system because I was so disappointed in the 2-channel music quality coming from my Denon 3310. Consider this: an AVR is designed to do many things well, a component pre-amp is designed to do ONE thing well.
The quality of the DAC is only as good as the quality of your analog output stages, the sound still has to go thru a volume pot. If you already have a component pre, I'd keep it until you buy your AVR, that way you won't have any regrets.