Tonally, if you're looking for a sonic match for your Mirage 7Si's speakers, and are mostly into movies, for the price range the Denon is going to make a fine match overall. HOWEVER, speaking as someone who'e sold Denon and Mirage both since '95, and has extensive experience with both brands, I strongly recommend you run your speakers as "small" on your receiver for sure! I think the 3803 is going to match the slightly veiled and rolled off sound of the 7si's. The 3803 is crisp and clear, and soundstages very well for a receiver, has good processing, and is clean. INfact, better than most any other receiver in the price range. BUT, like most any receiver, they're CURRENT LIMITED compared to even modest separates power amps!
You won't lose on the sonics of the B&K either, as it's sonically excellent for a receiver as well.
Still, I once did a comparison with the old Denon AVR5600(when it was king of receivers) running some Mirage M7's and M5's playing full range for both music and HT, back when DVD was just coming out. I compared the amp section in this big receiver(and the Yamaha DSPA3090) to the modest Denon POA8300 3 ch power amp to driver the same speakers(Mirage). The receivers could not properly drive the speakers!!! Using the receivers "pre-out's" feeding the Denon 125 w/ch power amp WAS FAR MORE POWERFULL, DYNAMIC, and CONVINCING! At the very least, the separates power amp seemed to have 3x's the power on tap to control the speakers over what the receivers internal amps possesed!..this has largely been my experience with receivers in general on most speakers systems of modest sensitivity.
Anyway, My suggestion would be to possibly consider finding a deal on the receiver if you can used, or even going down to the AVR2803! Then you can add a better amp for the mains at least! hope this helps. Good luck
