But it can...
Notice: this thing contains numerous modules that, back in the day, would NOT talk to each other or play nicely in the same cab. Voicing is on the upper two rows, control on the lower two. But you'd never have put Moog or ARP modules in the same build with the Buchla modules. And adding the Roland clones opens things up even more, along with a few modules from other manufacturers. In actuality, this turned out to be a pretty potent build, and I'm going to file this one for future reference. Plus, by the time I get around to building this, I'll probably have to change it, as Tiptop's stated that there WILL be further Buchla/Tiptop modules on the way.
And yes, a cassette deck is another source in this system...albeit a twisted sort of cassette deck with a chopper circuit and CV over speed.