ZP, you got it right... it's great right after a TS. guru, seriously it shouldn't be before your OD808, you really need to put it after... i mean, do whatever you want, it's your rig, but that's kind of like putting the wax on your car before you wash it. if it's hurting your high end you either have a bad unit or something else wrong. i'd never set it higher than about 11:00 though. the pedal does suck batteries pretty quick, compared to say a tube screamer... and when it starts dying it definitely adversely affects the sound quality. maybe you need fresh batteries more often, or a power supply?
either way, it's a noise reduction pedal.... you put it after the noisy stuff..... like OD808's. c'mon now, this ain't rocket surgery.