Very nice. What frequency divider are you using on the THCAD?
Is the THCAD mounted at the plasma end or the controller end? Mine is at the controller end but with the benefit of hindsight, it should be at the plasma end because the frequency output by the THCAD travelling across the interconnecting cable is much more immune to noise than a divided torch voltage.
Dependence on the Mesa THCAD board is not a concern at all in my view. It gives you robust state of the art A/D conversion specifically designed for the noisy plasma environment. Because each board is individually calibrated, its highly accurate and has a very fast response (we measured about 5ms rise time) so your THC is tracking whats happening now, not a few cycles ago.
For $70 its a steal!