Hi @Euripide! I'm very sorry for the late response. I've moved to Stuttgart, Germany and its been crazy.
I used some equipment to test this [gear]; effects loop 1 has OCD>Riot>MX EQ, effects loop 2 goes back to the PSR MT15 effects loops to add digital effects between PRE and POWER amp [hx effects back].
I was able to create the proper flow for my setup using the latest firmware [flow].
I created a starting entry with Left (A) for Magnetic and Right (B) for Piezo [input - mixer 1, input - mixer 2], adding some effects ONLY to (A) and leave (B) clean.
At the end of the chain, I created a Split Y [output - split y].
Has anyone come up with a fix for the PRS MT15's Clean Volume and Lead Gain pots? I think they use audio taper pots that really suck and makes it really difficult to control the levels. I'll add a Behringer MIC100 between PRE and POWER amp temporally.