You need to have the BS2 and the Monologue on different MIDI channels and use the Circuit to send only clock to both of them. Because neither the BS2 nor the Logue have a MIDI Thru jack, you need to buy a MIDI Thru hub like this:
https://www.amazon.com/MIDI-Solutions-Quadra-4-Output-Thru/dp/B0002GH8X4
This will take the output MIDI of the Circuit and split it between your other devices, allowing you to have each piece listen on one discrete channel.
In the short term, you can turn off the Program Change TX function on the Monologue in the Settings menu (Global, button 7 I think). In any case, because they both lack a true MIDI thru port, it's best to invest in a hub, because you'll need it to add more gear to receive clock (or sequences from the Circuit).
If you are looking for something more compact than the official KORG one, I can vouch for this one as being quite excellent:
https://www.amazon.com/dp/B01KLBE1SO/ref=cm_sw_r_cp_apa_i_9VYKFb0Q0GWH0?_encoding=UTF8&psc=1
Works for Minilogue as well as Volcas.
Okay, so I think I see the problem. Are you trying to run the audio through USB? The Monologue doesn't support that.
You need to use either the Output jack or the Headphone jack. Output is 1/4" mono (Tip-Sleeve), Headphones is the same but mirrored to stereo (1/4" Tip-Ring-Sleeve).
If you don't have anything with a 1/4" plug, you can use a 1/4" to 3.5mm TRS adapter. Example. This will let you plug a regular pair of consumer headphones in, so at least you can hear what you're playing, or you can use a speaker with an "aux cable" (the cable with the headphone style plug you'd plug into your computer).
Not really a KP3+ case... but a buddy of mine uses plastic handgun cases for some of his smaller pieces of equipment.
Something like this:
https://www.walmart.com/ip/Plano-Protector-Series-Four-Pistol-Case/16662942
Sorta in the same boat unfortunately:/ just bought it a couple months ago too.
I was planning to checkout some oscillators by Shoebridge next: https://sellfy.com/soundmangling/korguo/
His One/Two look interesting as well as a few others
Good luck to ya!
Trying to plug it into this so I can plug into a PC M-Audio M-Track Solo – USB Audio Interface for Recording, Streaming and Podcasting with XLR, Line and DI Inputs, Plus a Software Suite Included https://www.amazon.com/dp/B08Q1NJSBQ/ref=cm_sw_r_apan_glt_fabc_YRFGTSRWNAFEJFGT91K2?_encoding=UTF8&psc=1