I'll reply, if for no other reason than to give this thread a bump
I've not heard the sony, so my comments are restricted to the Denon and the Marantz. If you're AV/Music split is biased to AV, then the Denon is a nice little amp, does everything you're likely to want from a budget amp, reasonably punchy and with enough connections for the average front room. The Marantz is a more musical sounding amp (this is where Marantz focuses it's efforts in IMO), which still holds it's own at AV, though it may sound a little warm compared to the Denon (some people prefer this, so have a listen).
If this sony follows the trends of some of it's siblings, it will more than likely be quite competent, well connected, but never really excel in either area (av or stereo).
One personal note, the sony documentation will more than likely be the best of the bunch, I find Marantz and Denon both lack a certain something when compiling their manuals.
Hope this helps,
Tony
