The MXR looks like a good unit, you could try it in the MP1 loop, if so, try to adjust the MP1 loop gain knob (this is a dual ganged pot so as you turn up the input, the output goes down and visa versa, this is to maintain unity gain, level in = level out (albeit with a modified sound)) so there is no difference volume wise with the MP1 loop in or MP1 loop off on the patch (this ensure good gain structure in the MP1). The MXR is designed (from what I could tell (http://www.jimdunlop.com/files/manuals/M108_man_web.pdf)), to also add distortion (by increasing input gain to a guitar amp and eqing the sound) and be used guit > other pedals > MXR > Guitar (preamp) Amp in > speakers. You don't necessarily need more distortion with the MP1 , it's got stacks (but some like more
eg 3TM) but the MP1/3TM get it from the tubes, as you have EMG's you have plenty of grunt from the guitar, so, if it were me, I'd use the MXR in the MP1 loop, set it to crystal clean (don't try and add distortion/gain here) go for a scoop V setting (as Dante suggests) to start, keep the volume and gain settings such that turning the loop patch on/off keeps the same volume/level. I don't know how loud you play, but as you turn up the wick, how your ears perceive the sound changes (Fletcher Munchen curves). At low volumes, your ear/brain hears the midrange as louder (~1khz) and the bass and treble seems softer (even though they aren't, BTW this is why loudness buttons/contour knobs are on hifis, boost bass and treble), when the volume gets to 98db (loud for some, not for guitar
), the bass, mids and treb seem the same (balanced), above that (which is where rock guitar happens...) the bass and treble seem louder than mids. So if you run up a tone setting in the lounge, it will sound quite different when you cranked it up, so best to tweak the patch at stage vol if you can, then turn down for lounge. Anyway sorry to babble on, hope it helps...