I'm using an Xotic AC+ in the front of my MKV. While I totally agree with one of the previous postings about needing an overdrive pedal on a Rectifier (which is what I owned before the V) and not so much on the V, I love the versitility of the AC+. I like to use the lower gain side of the pedal on channel one for a slight overdrive, and use the dirtier side of the pedal just like a Tube Screamer. I use channel two on Edge with a gain around 11, so whenever I need a bit more gain (but not as much as I have on channel 3).. I dirty it up a bit more with the pedal. It's true bypass and is pretty transparent.
Anyway, just thought I'd throw it out there as well.