Well, i'm not totally sure what you mean about playing along with the MFs. I have definitely gotten some good, slowly auto-evolving patches going, but I don't have any particular trouble playing along with them. I mean they aren't necessarily in tune... is that what you mean? What is stoppping you from playing along with it? Do you just need a mixer to add some inputs? If all you need is a multiple and mixer then a CP-251 would provide it, but a lot more than you need also.
First off, the CP-251 is designed to process CV signals and not audio signals. That may answer your question right off, I don't know. It has NO audio inputs/ouputs. Some of them may be used to mix audio signals or to spread one signal to multiple outputs.
This is from the CP-251 manual available for download at:
http://www.moogmusic.com/manuals/cp-251.pdf
"The S + H module has 2 ins nd 2 outs. The ins are labeled IN and TRIG. Whenever the TRIG signal crosses a preset threshold, the voltage at the IN jack is sampled, and is held until the next time the TRIG signal crosses the threshold. The sampled voltage appears at the OUT 1 jack."
Basically, you can get a random step voltage very easily. It will step from one random voltage to another at regular time intervals determined by the LFO. Because of the way the CP-251 is set up you can just use one patch cord instead of patching a lot of those things. You can use the random voltage to control anything you want. One simple example is to have the MF-101 in self-oscillation and the S + H output into the cutoff input. You will hear random notes at regular intervals.
As far as getting it in tune you would need some sort of sequencer or quantizer, I guess.