Yup. I don't know the exact spec on the 770, but I know it has a MIDI OUT. Just hook that up to the MIDI IN on a rackmount or phrase sampler and hook the audio outputs of the sampler up to a mixer.
You'll also have to set the MIDI channels to the same channel to operate the sampler from the 770. Check the manuals or maybe someone knows more about the 770 and can help in that area.
As far as samplers go, if you want to use loops, phrase samplers are good and cheap (Boss makes some nice ones). If you want to use drumkits and multisampled instruments, you'll need a rackmount sampler or, of course, one the numerous software options. Emu, Akai and Yamaha all make real nice hardware samplers, good prices used too. I recently picked up a used Akai S2000 for $150.
Good luck
Stray