Denis,
I made the modifications you outlined earlier and it works great in soundmodem, VARA and Fldigi! PTT is triggered when the CM108 PTT GPIO 3 pin goes high, so I used the blue modifications in your diagrams above. The nice thing about this arrangement is that I can simultaneously run Flrig and soundmodem or VARA for remote control operation with just one cable between the PC and the DigiRig.
For your reference, here’s how to modify a cheap (~$2) CM108 sound card with PTT activation using the CM108’s GPIO 3 pin. I’ve made several of these (less the COS wire, which I didn’t need). I used a TRRS jack with the same pinouts as DigiRig so I can share cables. They work fine, but require a very steady hand to remove some of the SMT components as well as soldering. Modifying the DigiRig to do the same thing was easier, but still requires some careful soldering.
My home-brew sound cards:
Steve AG7GN