The guys at Best-tronics now have official MIDI Y cables for the PBC/6X MIDI output, which splits it into an input and output. These cables actually work with all Masterminds (except the original red display one), but they're most useful with the PCB/6X, which doesn't have a dedicated MIDI In jack
You can find them here:
https://btpa.com/midibs-ii.html?category_id=138
https://btpa.com/midibsr-ii.html?category_id=138
https://btpa.com/midibr-ii.html?category_id=138
You can find them here:
https://btpa.com/midibs-ii.html?category_id=138
https://btpa.com/midibsr-ii.html?category_id=138
https://btpa.com/midibr-ii.html?category_id=138