The keys are a little bit... soggier? But the sound is spectacular. But only the piano (and 80s synths, and the rhodes ep's); the Modx blows it away in every way, as far as I'm concerned, *except* not having built in speakers really hurts it. All keyboard amps I've tried are too muddy (including the Peavey's); I would instead ask you to listen on headphones, but if you need speakers use PA speakers instead. The QSC K10's and K12's (mark 1, not mark 2), or QSC CP8's. Or if you *have* to get something like a keyboard amp, the clearest i've heard are Roland PM100/PM200.
Did you notice that the DGX670 speakers crackle if you play piano only at full volume? THe p125 piano is a wide, solid sound, but with barely any dynamics, Through equally clear speakers, the Modx8/Montage blow them away... but most people don't realize just how clear built in speakers are. Keyboard amps (every one I've tried... Roland, Peavey, Yorkville, etc) are all way too muddy to me and kill the clarity and dynamics of the sound, *and* you lose a *lot* in mono.
Heck, even an inexpensive pair of studio monitors like HS7's ,or even ones that aren't as clear like KRK Rp7's or the Mackie MR624's would be *miles* better sounding than the KB3.
I mean, if you can? you should take the audio out from the Modx and put it into the aux in of the DGX670 and despite the buzz that comes from a 1/8" input, you should be able to hear how clear the MOdx8 piano actually is (yes Modx8/8+ are the same exact sound library)
Or try both with headphones to see what I mean
Mark
www.youtube.com/MarkWilburnTLM/Videos
DX7, CLP300, PSR60, Roland E20 + MT32, CVP309, PSRS970, Fender Std Strat, Squier RB3 Midi Strat, Ibanez SA262, Yamaha CG131, Fujiyama FC390, TUC-Kitty