Inferior Dacs? Inferior circuitry, inferior power supply and components.
If you're getting an AV Receiver around this price category for processing alone you won't notice the difference between something like a 3803 and an AX5i. I think the 3803 is as 'high' as you'll need to climb on this ladder...
the beauty of a 4550 is the sexy clean power you get but as a processor not bad as it has logic 7 from lexicon and 7.1 amplification so oodles to drive any extra speakers!
There was an HK AVR8500 in classifieds for £900
I'm not familiar with what you're using as a poweramp - but would expect that something like the 8500 in the classifieds would outperform it by a long way...
not much more than a new 4550!!!! Way sexier too but only 5.1 amps on board! new HK range is coming so either sit on your hands (hard i know) or snap an ex demo bargain.