Roland's have ALWAYS been backwards compatible... and the instruments ought to be CLOSE, at least. Thing is, with so many new and great sounds in a BK compared to much older gear (especially synth sounds), you will want to replace those dated kits and sounds with the newer ones...

And this is where Roland's SHINE.

The tools to easily replace sounds, effects, tweak velocity levels on everything from just a single drum in a kit to an entire style are the best in the business. They are so easy, in fact, that you WILL find yourself doing it, whereas most other manufacturers make this such a chore, few even bother, much.