I tested yesterday PAL TI99 connected with self made YPrPb-cable to OSSC (firmware 0.82). It works fine with my TV (lg). OSSC show that TI outputs something like 15.x kHz and 50.y Hz. I do not remember rest of the information, but can check later. First I thought what was wrong with the colors, but then I realized that automatic input selector chose RGB instead of YPrPb. This is not really problem. It is possible change manually or even save YPrPb as default input to profile.
Picture was excellent, the best I have seen with TI. ...and without any adjustments TI invaders worked great.