We run one. I'm not convinced it adds anything other than octaves of anything which muck up my bass. I know some guys really like it, though.
For bass, I've not heard one help. They either add mud, or lows that the speakers cannot reproduce anyway (most bass cabs don't do a lot below 60). And they mask real overtones and replace them with artificial overtones. For PA, they are junk, just like the other maximizers and exciters. When they first introduced it, they had a bunch of demo clips on the site. On every one of the comparisons, the without-with comparison sounded like CD-low rate MP3. When I encounter these in a PA, I patch around them, as I've never heard one fail to make the system sound worse.
Wonder if there's a way to run it so it doesn't get much in the way (other than removing it from the rack)
i use a dbx 120xp sub synth a lot, which is similar to the kosmos... i've always gotten the best results when using it in an fx loop, and sending only specific info through it. i've had great results with kick/toms, just electronics, or just bass, but too much results in a mess ime.
I just ran an outdoor gig today with mine. Most all stuff set at close to flat on the board. Kosmos running all knobs at 12:00 Set-up in stereo, with out the sub, function, this is the cheaper Kosmos, not the Pro, or whatever it's called. Sounds fantastic! Don't over EQ everything and you will have much better use of it all, on your whole system, I belive. Just got home, I'm pooped. Had lots of compliments.