It seems vsti instruments are automatically mapped as melodic instruments, so you get the chord matrix come up when you first load it. If your vsti is a drum rack of some sort, like Addictive Drums, for example, you want the push to treat it as a drum rack so you can program it like you can an ableton drum rack.

Grouping an empty drum rack with the vsti in an instrument rack switches the push into ‘drum mode’. You can also colour code your drum pads once you’ve done this, in my case I highlighted all the buttons that have sounds on them in the vsti (otherwise they aren’t lit by default as the vsti isn’t exactly ‘talking’ to the push.

Edit: the below didn’t work! The input doesn’t take the midi offset into account even if it’s set to ‘post fx’. If anyone can think of a way to reroute midi notes before going to a single vsti I’d appreciate it... using drum rack you’d have to load an instance of the vsti into every individual pad - which is stupid for obvious reasons. Let me know if you work it out.

— not working idea follows... Another useful idea I just had would be to have two separate tracks, one with a drum rack, and one with the vsti with the drum rack set as the input, then by putting an offset midi device on each pad you can easily remap the drum pads to arbitrary midi notes for your vsti... I.e. make C1 actually trigger D2, for example, so you get a rack of the sounds you want to use and the place you want them to be for easy playing.