Custom switcher to reroute guitar + bass signals

[rumblefuzz]

Hello everyone,

Not my first post on this forum (i think), but it's been a long time nonetheless. I mostly just look around whenever I'm doing a project, which isn't that often. This time something's come up that's a little beyond me, but I'm hopeful that it'd be a nice little project.

I need a switching system for a bass/guitar rig. Two inputs (one for bass and one for guitar) and two outputs (same), but with one stomp i need to send the bass signal to the bass output AND the guitar amp simultaneously, cutting the guitar signal. With another stomp I want to activate a true bypass fx loop only on the signal that goes to the guitar amp (that's the easy part).

I drew it up in illustrator quickly to make it a little clearer hopefully:


The problem I suspect I'll run into is that two separate rigs would interact in this box, which spells all kind of groundloop and leakage problems to me. I wonder if i can do this with a passive switcher, or if i need to go another route. I've been looking at this simple active splitter schematic: http://tagboardeffects.blogspot.nl/2014/08/amz-2-channel-splitter.html, which could work i guess if I split the bass signal that way. But I'd still make a ground loop between guitar amp and bass di? Another option is to incorporate a passive bass di into this box, thus giving me an option to lift the ground on that signal.

What do you guys think? Any help would be appreciated!