One thing I noticed is that Konami tended to combine the digital and noise for their drum sounds. For example, a bass drum would just be a sample, but when they'd play a snare drum they'd play a short sample and some noise at the same time.
It can sound pretty good when you do it that way, it just takes some experimentation to get the sound you want. The noise channel can give a snare drum a nice fade-out type of sound. If you only use a longer sample by itself, it starts to sound crappier as the sample's volume level gets lower.
Y'know, that's one thing NT2's site distinctly lacks.. some DPCM samples. Maybe it would be a good idea to get a bunch of nice-sounding samples and put them in a big .zip or something. But I haven't tried converting any for a while, I've been using the same ones for a long time.