What gear do you have? A Tetra and a Mopho Keyboard?
Turn off polychain when wanting to use MPE. Instead you use Tetra in Multi mode and Possibly Combo mode, use the same program on all four channels and enjoy playing a four voice synth with your LinnStrument.
If you have a Mopho Keyboard too then its simply a fifth voice. Connect using MIDI Thru from the instrument connected to LinnStrument to MIDI In on the other instrument, align the channels so that they are next to each other and make sure that the channels used match those used by LinnStrument's note output. Check its manual and/or with a MIDI monitoring program.
Program changes are left as an exercise for the reader! Obviously its all about understanding the controller and synths that you use.
Good luck with it!