Don't know about a replacement for the Digitech foot switch, six pin lead sounds very Digitech proprietary.
Any midi foot switch (e.g. ADA MC1 you have for your MP1 ?) will change programs (5 pin midi in) so use a short midi cable from your MP1 midi through to Digitech midi in and the Digitech will get the same midi numbers (patch change) when you change MP1 programs with the foot switch. Or MP1 midi out will also work and sends the change also if you change MP1 programs from its front panel. MP1 midi out has a midi change table attached to it (xxx=yyy) so you can map MP1 program change numbers to any other midi number.
If the Digitech handles midi continuous change (CC), the the ADA MXC pedal with CC pedal and quad switch will work even better. Or the Behringer midi foot switch is very versatile and about the cheapest around I think (MikeB knows how to drive one, though it has lotss of options so could do you head in
).