I have several ways of implementing polyphony. One is I just feed my polyphonic digital piano into the modular via an input module and use the modular to modify the already polyphonic audio. I have the Bastl 1983 as well, but I also like the AvonSynth Midi to CV module, which is affordable and easy to use and gives your 4 channels of gate and CV + dedicated mod wheel and aftertouch outputs (I use a Nord Wave keyboard which has aftertouch). The Bastl will give you aftertouch but only in mono mode I believe. But of course it has a number of other features the AvonSynth doesn't. Another way I implement polyphony is with the Expert Sleepers Disting EX + midi breakout, currently I'm using the sample player in the EX and then feeding the output into other parts of my modular.