There's a thread elsewhere on this site where I do go into a bit more detail. But I'll recap some of my observations here.
The Denon sounds a lot better with Redbook, IMOHO. Cleaner, crisper, with a *seemingly* quieter background. But the improvement is even more pronounced with DVD-A & SACD. I feel the Denon is a touch warmer but more detailed at the same time. It's hi rez perfomance is simply more liquid & musical. I'm reluctant to resort to the Purple Prose that so often passes for critique, but it just flat out sounds better.
One problem with the Pioneer is the lack of bass managment. The Denon offers full bass management in digital domain, and unless you have 5 large speakers, this is a critical ommision for the DV-45A. Sure, if you have an outboard crossover, something like an Outlaw ICBM, this wouldn't matter. But MC music often has serious bass mixed into the center & surround channels, and you'll never know how good they can sound until you've heard it with the system configured properly.
Lastly, the Denon has better video performance. The Pioneer is good indeed, but the Denon seems to have a tad better color & detail. Plus, the Denon reads thru a memory buffer- this is a wonderful feature that prevents the pause or "hang up" you get when the DVD switches layers.
I'd suggest that if money is an issue, you might want to check out the Pioneer DV-563A or its new replacement. As old as the '45A is, I suspect the cheaper yet new machines offer similar perfomance for even less money (in fact, around $150). The new Pioneers also seem bullet-proof, and will play any disc including unfinalized CD-Rs and DVD-Rs where the burn failed.
BTW, one final issue I had with the '45A is the supplied remote- it has a very limited angle of operation. You must basically have a straight line of site between the remote & player. The boneheads that designed the remote recessed the emitter deep inside the front of the unit instead of near the surface. That was a major flaw to me as I sited the player directly behind my listening/watching position. And unlike the Denon, the Pioneer remote isn't powerful enough to bounce off the screen in front of the room and operate the gear at the back. Just an FYI.
