I use a MOTU Ultralite. It serves as an 10 in 8 out 8 buss stereo mixer for minstage, 2 other keyboards, in ears monitors, FOH fead, stage monitor, vocoder, backline feed, etc. Very flexible for any need. Throw in the excellent compression and leveling to fatten up those other keys and your sound kills. You can save multiple configs so it can instantly be a recording interface too.
It was worth the extra expense as it cut down on space, weight, and setup.
Hope this helps,
Hooch