Well, I can't really comment on those exact components. However, I have related components, so Ill throw my opinion out there!
I have the Denon AVR-5700 receiver paired with the Klipsch reference 3 series all around (RF-3s, RC-3, and RS-3s).
I love the sound these two provide. Denon is known for having "warm" sound. The warm sounding amp teamed with what some (not me) think is overly bright Klipsch speakers makes an absolutely perfect match! I'm pretty sure you will find the same with your 5600.
Denon is a highly respected manufacturer. When it comes to receivers, Denon is always one of the best out there. In my receiver's day, it was known as one of the best receivers on the market. The major magazines held it and the Marantz flagship as the best you could buy. the 5700's successor - the 5800/5803 are currently held as one of the best receivers money can buy today. I don't know too much about the 5600, however, judging from the numbering, I would assume it received the same level of respect in its day.
As far as problems go, I have never had an issue with my 5700. I will soon be upgrading my system again. I plan on upgrading my set of reference 3 series up to the 7 series all around. I will also be buying a heavy duty amp in my move to seperates. However, I'll probably keep my 5700 for another year or two after that, using it as a pre/pro with the new amp - its that good of a unit!
Anyhow, I searched Denon's webpage, but couldn't find anything on the 5600. However, just on my experience with Denon, and their awesome reputation....I would feel pretty confident. And if the price was right...sounds like a solid foundation to your Home Theater (or home theater to be).