Yeah a minimix would solve your problem. You wouln't want to digitize your nice analog tone.
But. If you want to use the chorus of the M300 would you want it parallel?
I have a Dynacord Leslie in my rack. I want to use that in series. With the Rocktron
I can choose if I want to run a patch in parallel (Reverb, delay) or in series (Chorus, Flanger,tremelo etc)