It should be noted that the Line6 M5 (and IIRC other Line6 pedals with expression inputs) require...
...a TS cable 10kOhm.
Most every expression pedal on the planet works with TRS cables.
Haha yep I've learnt that one the hard way. When Line6 say "Compatible with standard expression pedals" in their manual they mean "Only compatible with six known exp pedals, two of which are made specifically for Line6's unusual expression implementation."