Although I said the SCLX8* models will work better (and will work far better than their cheaper VSX receivers, which was my point), I'd still recommend switching the budget round (or using it more wisely) - £2k on a receiver and £6k on a speaker package will get you great sound, but the speakers can only perform within the quality parameters of the AV receiver used. I've done just that recently, and I now have better quality coming out of old hi-if speakers than my previous dedicated AV speakers. That's not to say that there was anything wrong with the speakers I had, it's just that they didn't have sufficient quality feeding them. If I could've kept my speakers, they'd now be sounding stunning beyond belief.
The amplifier can only amplify the quality of signal it receives, and a speaker does (and is limited to) what the amplifier tells it to do. Processing and quality of processing is all important (just as it would be in a hi-fi system.