I think you'll be hard pressed to find 6X feedback.
As I seemingly spend half of every day helping people with their 6L80E/6L90E installs, that might be a possible explanation. The GM 6L is awesome. Clutch to Clutch operation for super quick shifting, internal TCM, and readily available. ...And if you want 6L feedback, just go drive a TAPshift vette, then imagine it shifting and launching more quickly after custom calibration.
The 6X is bolt in, the 6L requires that you apply your thinking cap and have your ducks in a row. The 6X is expensive. I've heard reports of 6L's for $1500
with TCM. You'll then spend money on the right harness and, to achieve your listed goals of low parasitic loss and snappy launches, the right torque converter.
