The XY I/O uses two 3.5mm TRS jacks, which accept insert cables to provide send/return capability to a pair of Pedal I/O’s, or additional stereo inputs (or outputs) to a pair of Mixups, or one of each.
A third 3-pin Link connector on the back panel allows the X and Y jacks to access the L/R (or Send/Return) jacks on a single connected module or case without needing a stereo cable.