I use my MXR M-80 with my amp, never tried it with a power amp. I leave it on all the time, and use the channel 2 with very little distortion and the blend knob set to 9 o´clock. Sound very good with my Jazz Bass, very consistent, I don´t think it´s very transparent, but its equalization is very versatile.
When using my amp I only use the M80 to change my tone or boost the volume if needed, and the distortion channel If I’m going direct to the PA then I’ll adjust the EQ as required and still use the distortion when required. I've tried it straight to the power amp and it works well but don't usually use it like that.