First thing i did with it :
a chain with several sample players contained in mixers, loaded with one-shot drum samples, each being triggered by one of the “virtual” trigger from Teletype.
Sequencing done by the TT.
Result : a drum kit within a single chain, without any cable, and with minimal amount of work on the ER-301 side (no need for making a wav file with several hits, or use of the Bump Scanner method or whatever).
Then, a voice synth driven by the TT, also with no cable.
You could make songs with just the two modules, actually.