I believe that the FS-6 uses the exact same mechanism as the FC7, they look identical and feel pretty similar.

The main difference is that on the FC7 the switches are closer together, which for your intended purpose is far better. The FS-6’s switches are just a bit too far separated for one foot to quickly press both one straight after the other for a quick up/down without quite a bit of motion. The FC7 allowed far faster transition.

The FC7 input accepts any simple switches of the correct polarity, so the world’s your oyster if you want to try to build something custom. But before you start, it’s worth starting with your feet! What’s a comfortable distance between them to quickly go from one to another? And what’s a good geometry? Personally, I think that something laid out a bit more radially, a bit less linear than the FC7 would allow you to pivot your foot on your heel to go without looking from one switch to the next. The FS-6 looks like it needs the whole foot moved to go from one to the other.

If I remember rightly, the FS-6 switch mechanisms screw into the case, it might be worth investigating fabricating a different case for them to get them MUCH closer together.

By the way, on a different note, have you explored using the D-Beam to turn Parts on and off? I find that incredibly useful (probably the only non-gimmicky use for the D-Beam!) to strip away the backing and go to just bass and drums for a section, or to drop out the drums for an interlude, etc..

Combine it with the Track Mute button, and you can get some quite complex remixing. The Track Mute assignments are global, but what the D-Beam does is per Performance. If you aren’t already hip to it, give it a try!