Hey bigjd, there are others here who run their MP1 similarly, not my preferred patching idea/gain structure (though I get why you'd want to, and why people do). Is the GSP loop stereo ? if not even more reason to not do it apart from the input drive aspect. Are you using GSP out to MP1 or loop out to MP1 ?
IMHO, and I've done some testing (posted elsewhere here with MikeBs GMaj), breaking your analogue signal path by going through digital gadgets (unless the have true analogue pass through of the dry signal (some older units do)) sucks tone/dynamics/energy.
Here's the options I spose:
Guit > GSP > MP1 > GMaj > Amp(s) > cabs (looks good on paper but wont sound as good as keeping all analogue path from guit to cabs), So don't no what the GSP does to the signal but I know the GMaj inputs turn it into digital and it sounds lots better if you mix GMaj into the signal path, not go through it (you loose GMaj CC options like master vol, noise gate) but sounds heaps better using a parallel loop (use small mixer with at least 2 FX sends, ART Split mix etc).
Personally, the "only" thing I'd consider before the MP1 is a wah pedal. The MP1 wants to get a guitar signal at guitar impedance/vol, anything else I mix in using a small desk, mine has 3 FX sends so I feed my quadverb L/R and my IPS33, they both return down 2 channels each (pan L/R) and I mix in the amount of FX I want into the analogue signal, desk L/R to stereo poweramp > 2 x cabs.
So my advice (for what it's worth) is to start with Guit > MP1 > st amp > cabs and get that sounding how you want (I suspect will blow you away with how good it sounds without the digital conversion(s)), then work out how to mix in GSP and TC, small desk with 3 sends is one way (best). but you could use the ART Splitmix solution (developed by MikeB and myself...), variation to have GSP sounds also go through TC (easier with desk option BTW) is put TC in GSP loop (or GSP in GMaj loop ? does it have one ??) and mix result into signal path.
Hope this helps, cheers R