I’ve got no experience with any MPCs (it would probably be good if you mentioned which one you have, btw) or the MPD, but I think you can set the MPC midi outs to be thru instead, can’t you? If so, I would go MPD midi out to the MPC midi in, one output set as a thru going to the OT in, and the other going from the other MPC out to the MPD in to send clock/transport (not sure if this is necessary, since I don’t know if the MPD would end up being the master otherwise). Not sure if that will work, however.
Is there any reason you are not using the OT as the master? I would assume it sends more stable clock than the MPC. Setting the MPD out to OT in, OT thru to MPC in seems less complicated and more accurate.
should just be a case of connecting MPD out to MPC in and MPC out to Octatrack in. ensure midi thru is enabled in the MPC midi menu, and you’re good to go