I found a solution. I don't know how useful this will be for other midi devices, but for the DTX M12? This works for my needs
I thought about how the GateTime setting on the M12 went to a full footsplash sound when set to 0. There is also a TRGMonoPoly setting in the M12, and setting this to "mono" while playing the midi note for the foot splash for some reason produces only a "chic" from the drumit 3.
So on the M12, I chose the "HHCL" function and set it to mono with midi note B1. Then I went to the "HHSP" function and set the Gatetime to 0 and set it to the same exact midi note, leaving it set to Poly.
It's not quite how 2box intended it but, I am getting consistent chics and really have to kick the thing to get a footsplash, which typically produces a chic and splash at the same time, but, works enough for my needs as I mostly wanted to nail down a consistent "chic" and full range of the RHH135, and in that regard, doing so via midi from the M12 feels infinitely better than my results trying to use the RHH135 into the 2box hihat inputs.
It is a night and day difference. I can mute the cymbal without playing a chic. I can play chics as fast as I want. There's a specific way to hit the pedal to get a footsplash. I have the full range of my RHH135 with no calibration or tweaking required.
Time to start having fun with my 2box/m12 hybrid kit. It's hard to express how sweet this setup turned out to be, and I've already done the SD extender mod.
I thought about how the GateTime setting on the M12 went to a full footsplash sound when set to 0. There is also a TRGMonoPoly setting in the M12, and setting this to "mono" while playing the midi note for the foot splash for some reason produces only a "chic" from the drumit 3.
So on the M12, I chose the "HHCL" function and set it to mono with midi note B1. Then I went to the "HHSP" function and set the Gatetime to 0 and set it to the same exact midi note, leaving it set to Poly.
It's not quite how 2box intended it but, I am getting consistent chics and really have to kick the thing to get a footsplash, which typically produces a chic and splash at the same time, but, works enough for my needs as I mostly wanted to nail down a consistent "chic" and full range of the RHH135, and in that regard, doing so via midi from the M12 feels infinitely better than my results trying to use the RHH135 into the 2box hihat inputs.
It is a night and day difference. I can mute the cymbal without playing a chic. I can play chics as fast as I want. There's a specific way to hit the pedal to get a footsplash. I have the full range of my RHH135 with no calibration or tweaking required.
Time to start having fun with my 2box/m12 hybrid kit. It's hard to express how sweet this setup turned out to be, and I've already done the SD extender mod.