Welcome to the forums jaimisUK.
I say this a lot, but have a listen to the Tannoy Arena if you can, as I found it to be a very good package, (I thought better than the MT-30 when I demod; I never listened to the MAs, but they're supposed to be very good). The strong point on the MT-30 was the sub, but it didn't really seem to be any better then the Arena one, and the satellites, for me, were lacking at high frequency, which also affects detail. The KEF 5005 satellites were very good when I demod as well, (though I still think the Arenas shaded it), but the sub lets it down, especially for music.
In terms of amplifiers, while I haven't heard the SR6003, I can say that the SR6001 that I have is very good to my ears. I've been really impressed with it for both music, (using its DACs), and film, (only from DVD, so no HD sound, as I haven't got into BlueRay yet).
I've read elsewhere that the SR6003 is a rival to the RXV1900 in sound quality.
It does seem to be odd that when decoding onboard the Audyssey doesn't kick in. The room equalisation increases the sound quality a lot for my room. However, you can always get a player that decodes HD audio onboard and feed it to the amp as LPCM via the HDMI, and you're still getting the same HD sound. The SR6001 has no onboard decoding so that's what I'll be doing when I go BlueRay, and it also means the commentaries and stuff can be mixed into the BlueRay sound which isn't possible when decoding on the amp.