For anyone who doesn't have an SF-2, I can't recommend them highly enough! They are truly the magic box that provides the missing ingredient to the sound you are trying to get. I use mine to mainly get more punch out of my rig, whether I'm using my full Eden stack or my Fender Rumble 350 combo. I can dial in the punch in any room with about an 1/8th turn of the frequency control on the low channel, then use the dampening ratio to either fatten up the bottom or get rid of boomy bottom in some rooms. Then I use the high channel to give me an edge on the highs in high pass mode, then flip the switch to low pass mode to get a really nice midrange tone when we play Journey songs that need that sound.
$630 is a great price for this amazing piece of equipment! They list for $1675 new & are very hard to find used.