I did tell the M13 that FX1 and 2 are pre FX loop. That way I can have my delays and reverbs in the loop on FX 3&4.
I must say upon first switching on, I hated the distortions and overdrives. However, after very little tweaking, you can get pretty decent OD's and Distortons. Above all, the main thing for me is how good the noise supressor is. I had all analogue pedals with my Big Muff pie in the loop of a boss NS2, and the problem was every venue had a different earth and I would end up cranking the noise suppressor so high that all the dynamics would die.
With the M13 I have dead silence no matter how I crank up the distortions. Its a brilliant unit. Also I do not know if going through a valve am makes the difference however my amp is always set clean.
Very good unit.
regards
Jim