I use my Minilogue audio in with a Roland sound canvas SC-55. The Minilogue midi out goes to the SC-55 midi module, and the midi module audio out goes back to the minilogue audio in. If you use clean GM instruments such as a saw wave or string, and make sure chorus and reverb are off, you can effectively make the midi module almost like a 3rd VCO. The trick of turning down the 2 VCOs on the minilogue all the way is very useful to see the wave you're sending from the SC-55 on the Minilogues built in oscilloscope. It can give a nice 3 octave option too, since the GM module will stay in the octave that corresponds to the second from the top (of the four octaves on the minilogue VCOs). Alternately this lets you get a thicker 1 or 2 octave sound as well.
Added bonus, if you save your minilogue patches to the slot number which corresponds to the midi instrument number in the GM standard you wish to accompany it, rolling through programs in the minilogue brings the SC55 programs along with it (up to 100 slots). Else, if you set the minilogue program 1st, you can change the midi module to whatever wave or instrument you want to accompany the minilogue VCOs.
You can set up 16 instruments on the midi module, making midi channel select on the minilogue an option for having multiple instruments ready for supplimenting your minilogue VCOs on the fly.
Also you can assign multiple instruments to midi in 1 on the midi module, so you can feed a layer of vocals, keys, and strings for example all to the minilogue in as the 3rd voice source. Doing so divides the polyphony of the SC-55 but you won't go under the 4 note poly of the minilogue unless you assign more than 6 instruments, as the sc55 has 24 voices.
