I have quite a similar issue with HX Effects connected with 4CM to my Boss Nextone Artist.
when I use and activate an effects loop block in my chain, the output volume drops drastically and the tone gets much brighter.
even when I put nothing but the effects loop block in the chain.
If I disable the block, the output volume gets back to normal so it definitely the EL that mess things up.
I tried many combinations of send/return levels, mix, inst or line setup, small things change but I don’t get any sound close to the one when EL is not engaged.
I thought the effects loop would be totally neutral.
what can I do?
Thanks