Hello,
Well I eventually went for the SR6003. I must say that, from a sound quality perspective, it is excellent. I would however state that I do not have great deal of experience on which to provide a well grounded assessment. But, compared to the Denon 2309, the improvement is night and day. The sound is a lot more detailed with greater separation. The SQ from the denon was muffled/sluggish/flat by comparison. Considering that these two recievers are now at the same price point the marantz is excellent value for money.
On the down side (still working through the manual) the marantz probably does'nt have the same feature count as the denon e.g:
1. No Dynamic EQ (the marantz does have Night mode and there is a HT-EQ option, but I have'nt tested this yet),
2. You can't apply different crossover frequencies for different speakers (i think you could with the denon),
3. The crossover setting will only go down as far as 60hz (the kefs appear to have an initial spike at 40hz I wanted to address). I'm also unsure as to whether the Audyssey optimisation effects frequencies beyond 60hz.
4. I do'nt think you can apply the audyssey EQ optimisation to a HD sound input (although it looks like you can apply the settings manually to a 7.1 profile).
However, the marantz does have a GUI which makes the setup a lot more straight forward. For example, you can see at a glance which inputs have been assigned to what. There is also a 9 band equaliser (which allows you to see what audyssey has applied) which helps in modifying the user defined profiles. There are also some options to provide further customisation of some of the DSP modes.
I would however reiterate that the SQ of the marantz is excellent and a massive step up from the denon both with music and HT, but particularly music. Build quality is an improvement also. I also like the option of using the USB (pen drive) for music.
Not sure if this helps! I did'nt get chance to listen to a Yamaha unfortunatley. I was put off by the opinions of the "Yamaha sound"