Hi,
I think you are going to need an external mixer, since in addition to the audio outputs of each voice of your eurorack, you have the audio of the minibrute. If you want an external mixer, you basically have to take two aspects into account. That it is able to handle the hot audio levels that eurorack generates and that it has enough tracks for all your voices (I see at least 5 in your rack) plus the minibrute.
If I were in your situation, I would mount a mixer in the case, so I would only have two audio outputs, modular+minibrute.
Modular Tesseract has an economical solution with good features.
This is the 4 stereo channel module with 2 send/return and mutes (12HP).
https://www.modulargrid.net/e/tesseract-modular-tex-mix-4-stereo-channels
This is the output module with outputs for monitors and headphones (8HP)
https://www.modulargrid.net/e/tesseract-modular-tex-mix-master-section
The good thing is that it can be expanded with more 4-channel modules.
I have 4 stereo channels + 4 mono channels in my case.
For now, and if you are not going to use so many channels, and you want to use less HP's, you can mount a Happy Nerding 3xMIA (6HP)
https://www.modulargrid.net/e/happy-nerding-3x-mia-black
If in the future you need a 100% audio mixer, you can reuse the 3xMIA as a CV mixer.
To connect the guitar you need an input module with audio level control. It is recommended that you incorporate an envelope follower that generates CV according to the incoming sound.
There is a tight budget option that meets those requirements.
https://www.modulargrid.net/e/doepfer-a-119