That depends on what you're looking for. If memory serves, the 5600 has a bit more power than 3802, but it doesn't process DTS (I could be wrong about that). It's also a 5.1 channel receiver. It's built in DAC is older.

I don't think you would gain much by going the 5600 route. What is it that you're looking for in your upgrade? Is it features, power, better sound fidelity?

If you are looking for more power why not look for power amps to connect to your preamp outputs. The Denon AVR-5600 has 140 watts compared to the Denon AVR-3802's 105 watts. You really need to at least double your existing amplifier power to realize much of a difference (other than possibly the quality of the watts). Hence, you should be looking at at least 210 watts per channel, but you can get that by adding power amps to your existing system and not replacing your receiver.