| I've gotta say...
I don't think it's a great idea.
Admittedly I've never tried it for upright, and I don't own a GK rig, but
I've tried bi-amping in the past with electric bass (SWR, Pearce, Ampeg, GK and seperates) and invariably what happens is some funny stuff around the frequency that you select as the x-over. For electric some people may like this as a way to 'scoop' the sound, but for most acoustic players this will only take away whatever "natural" sound you might be lucky enough to get out of your pick up.
Active crossovers in controlled environments like PA systems that are installed or studio monitors that live in a control room are certainly a mainstay, but that's because they are "tweeked" to perfection. Really hard to do that with an amp that's moving in and out of different rooms all the time. As for the GK system i think that this feature is really a vestige of the old days when no one built equipment that was small and lightweight and had enough dynamic headroom for bass. Nowadays many manufacturers (GK included) have solved the problem and tiny cabinets with passive crossovers are loud enough, clear enough, light enough and natural sounding as well.
2 cents. I hope you can find someone with experience with this specific application before you buy one. | 
