Thanks for the post S100
Nick -- just to let you know how I got on...
Spent an hour and a half in Superfi today listening to the Yamaha and Denon with various sources. They didn't have the Sony in stock, so can't comment on that. They also threw the Onkyo 607 into the mix, but I thought it was a bit of a slugger (it punches really hard, but wasn't so refined), so I discounted that one fairly quickly.
In my humble opinion, the Yamaha was more forceful and exciting, and the Denon more refined and dragged up greater detail. For my purposes the Denon was ultimately the better choice, hence I ended up buying one there and then. I could see the Yamaha really upsetting the neighbours and the Denon sounded a touch warmer and more articulate through the midrange, so this might be exactly what you're looking for based on your earlier comments. The Yamaha is still a really good amp, and it was a very close call between the two. It was simply a case of the Denon suiting my needs better, rather than concluding it was a better receiver overall. Plus, the Denon was £70 cheaper, and a bit prettier to look at (if that's important to you).
Don't know if that helps? I've got wait till Tuesday now for it to be delivered.
Incidentally, Superfi told me that they will exchange for another receiver of the same or greater value if I'm not happy after I've had time to have a thorough listen at home. All in all, they were very helpful and let me audition all three receivers in a dedicated room with current model B&Ws, so I think I got a pretty good impression of how each would compliment my own speaker package. All in all, thumbs up to Superfi!