Ahh gotcha yeah,(sorry i wasnt looking at the unit when i replied) I tend to use the MONO for when im killin drums and use the stereo for mix bus. (its really a matter of taste, but there's definite sonic differences). I feel the mono acts a bit more aggressive, which isn't what I'm lookin for on the bus.
For mix bus duties, i tend to leave the HPF off as it does effect the sound quite a bit. (i use the T2 for drums though, really brings out the cymbals). I also tend to be VERY conservative with all the settings, ala 2:1, .3 attack (don't want to kill ALL the transients), auto release. As far as the threshold goes, i bring it down to where I'm JUST starting to hit the peaks to put that glue in place. My philosophy on bus compression is "if you can HEAR it, its too much".