[TurboWS6]

What does the car do on the transbrake?

If it's making 1 psi on the footbrake without the two step at part throttle its doing pretty good, you really need to be able to open the throttle body up because the extra air will really wake the turbos up. The only why to do that is with a two step set just below the 3500 rpm limit.

Your second option of using the synergy for the footbrake, and transbrake to the moon will work but it is going to stress the drivetrain pretty hard namely trans temp, but as long as you got a good cooler and a way to monitor the temp you should be fine. Car will probably go up to about 4K on the brake as turbo converters really tighten up as you go up.

Make sure your wheels are pointed straight. lol