I just tried to start a TPA table from PinballX with the default settings for TPA. Steam does do "something", and something launches, but then nothing happens until the timeout runs out, then I'm returned to PinballX.
I think I have some reading comprehension issues: Is it possible to launch specific TPA tables directly from within PinballX? If so, what's required beyond the default options in PinballX's TPA section? Some people mention external launchers, but others say that built-in TPA support should be enough, so I'm not sure.