mcouter,
I have only used the KB37 a couple of times, but I can already tell you that if you're looking for just a controller, you're probably better off with something like m-audio oxygen 8. The KB37 doesn't really feel as solid as it should. The build of it is kinda lightweight and hollow, almost like they stuck a bunch of features on a $50 Casio. The keys are semi-weighted but they feel kinda "plasticy."
The unit as a whole is great for me because it is an all-in-one deal (keys, guitar, bass, mics), but since you already have Toneport for guitar (and probably a decent setup that you use for recording the other inputs) you may want go with something that is less expensive and feels better.
However, if you want everything in one compact unit, it's great. And I really don't care about the keys feeling great (they're not that bad).
For the price tag, it's a good deal for all the features, but just buying it for use as a controller would be a mistake.