SCott,
First of all, the audio buddy has mic inputs AND line inputs. It's a TWO trick pony.
Secondly, I prefer to use the rca outs, so the kb monitor is separate from the main. I hear no difference in tone or quality, just makes it easier to make "me" happy on stage.
This is a very well made unit - all metal construction, but super tiny. It may even velcro to your stand or sit ontop of the kb with some rubber feet.
I'm going to use it this week and I'll tell you all about it.