Hey Jaster, it seems to me it's either a gain structure/matching problem or a connection problem. First check top switch is in Line pos not Inst as this changes the MP1 outs from Inst lv to Line Lv (to plug into guitar amp (Inst) or poweramp (Line)).
The rear jack (if not modded) is balanced TRS Line lv. TS jack should work but to check, use -10 on 1101 send / return and try the front MP1 input, and set top switch to Inst Lv for MP1 out to 1101 return.
Does the 1101 have diferent level settings for the send/return/mix in its patch settings ? I suspect it should so that may also be the issue. While you can run the MP1 in a loop like an FX or dist stomp box, that's not quite what they were designed for as you are driving the MP1 input with whatever input gain settings selected from the 1101 and then distorting them more (not good gain structure)
Another approach, "Y" split your guitar into 1101 in and MP1 front in, MP1 outs A/B into 1101 returns, this will pick up any 1101 FX that come after it's loop return for MP1 and mix it in with overall 1101 sound. You can then select various mix options by setting up different patches in 1101 and MP1 selecting various sounds and FX/Dry mix levels. This way you can program blank (zeroed) patches in MP1 when you don't want it in the sound, conversely set up 1101 patches with no (zeroed) input to just have MP1 + 1101 FX (and anything in between). My 2 cents worth.
Plenty of comments from me re maintaining analogue signal path elsewhere LOL
. The difference is quite obvious in a studio set up with good monitors or when you play at stage (loud
) volumes. But each to their own
A third approach may be use a small 4 channel mixer with 2 aux sends, again "Y" split 1101 and MP1 inputs (and control with patch settings). 1101 > ch 1/2, MP1 > ch 2/3 (pan hard L/R), aux 1/2 to 1101 returns then mixer L/R out to power amp.