Actually, the Korg PA3x has a FULL featured sampler, with data compatibility (mostly) with the Korg Triton series, which opens up a vast library of world class sample libraries. So importing drum kits in is very doable.

And no, while it can't actually stream off the HD like Ketron's do (mind you, I don't know if user made drumloops stream or have to be loaded first on the Ketron either), it can do the exact same timesliced drum loop thing that Ketron's do.

The main difference is that Ketron do the work FOR you, and for the most part, if you want to do this on a Korg, you have to roll your own.