<font color='#8D38C9'>JMOHO, but the Denon has more detail and is a bit "warmer" sounding. One huge advantage the Denon has is that is has superb bass management for both DVD-A & SACD (although the digital channel delay/distance settings don't function with DSD sources). This means that if you don't have pretty large speakers capable of some real bass, you will simply miss out on a lot of low frequency stuff if you go with the Pioneer.
I'd say aside from rythmic drive and detail, the Denon is a bit more transparent and "effortless" sounding that the Pioneer, especially with SACD. This may be due in part to the fact that the Pioneer converts DSD to PCM when decoding SACD- but then again, the DVD-A performance is better, too, so that can't be the whole story.
As a CD player, my DVD-2200 sounds better than my Denon DCM-380. It particulary outperforms the carousel with MP3 playback (comparatively my '380 sounds broken; maybe the firmware needs updating). At any rate, I don't think it's my imagination, a couple other people have made the same comment after hearing my rig. It's not just that particular unit, either. I've compared an older DCM-370 as well as my old Phillips player, and the DVD-2200 sounds better.
My advice to you is buy the Denon. It will probably cost a bit more (the DV-45A can often be found around $375 nowadays) but it's worth the extra money.
That said, the Pioneer is very competent with great video quality. I wouldn't have felt I was missing out had I not heard the Denon, and even then it's not like the Denon makes the Pioneer sound unlistenable.
BTW, the '2900 & '5900 may sound even better, I haven't ever had the chance to compare. $625 was about the most I could spend at the time I bought my player, so even if the upper models are better that'll have to wait awhile for me.</font>