I have had rotel amps and have looked seriously at Adcom, and I don't know that there is much difference between the two within the line. Cables can make a big difference, but I would look at the source first. Cable merely transmit signal. Some do it better than others, but if you have harshness like you mention, it's more likely to be the Denon. Sorry!
Better cables might tame some of the harshness that is introduced by the cables, but better cables could sound even more harsh if the issue is the Denon. Borrow a CDP from a friend and see how much difference it makes. Less expensive gear is built around compromises, the ones you hear might be part of the design inadequecies of your gear, or the cables. It's difficult to point out the source of the problem without actually swapping things in and out.