I have the Marrantz av7005 and am fairly happy with it . It's a 5.1 proccessor . The other models above it simply provide you with more output processing options like 7.1 and 11.1 .
I've had one issue with it , when in the network mode at some point I get a green flashing on my flat screen as I'm changing songs. By resetting its internal processors it seems to fix it, but temporarily . Other than that its all good . Great sound and a nicer GUI than my yamaha .
i agree with the reviews , the ir sensor could e a little better as I find I have too aim at the av7005 a little more accurately than you should have to .