I've owned three HK receivers, I currently own a HK amp, and recently purchased my first Denon receiver the 3805. I like HK a lot and wanted the 7200 but it's such a monster it wouldn't fit into my HT shelving and didn't have 3 component inputs so I didn't but it. HK tends to put their money into amps and power supplys where Denon, Yahama, and others provide more bells and whistles. If you need or want the bells then maybe a HK is not the product for you. But if want want nice sound check it out. I have not heard the 635 but have listened to the 2805, which of course sounds similar to my 3805.
Compared to my HK AVR85 my 3805 is similar in power and sound with the Denon having a more detailed sound, I'm hearing more information from it. The 85 was a first generation DD receiver where the 3805 is several iterations up the evolution chain so I expected as much. I have two friends with the HK 7200 and it sounds fantastic as well. I'd listen to both several times and then make your decision. You can't go wrong with either. You may also want to check into buying a refurbished unit. I've do so with both brands with no problems.
Good Luck which ever way you go.
