Thanks to all for answering the questions before I could get to them. Appreciated.
As for the parts on the back board that are different for the TXo+ - they really don’t matter much at all. I’m doing all new TXo with these values (raising the lame single-pole filter cutoff to match with the TXo+ sampling rate). As described in previous posts, you will need additional filtration regardless if you want to get a pure-ish sine out of the oscillator mode. Once you go into other waveforms, the aliasing is pretty much baked into the sound (though I do use PolyBlep to reduce it on the saw and square waves).
There will be some TXo+ upgrade kits - though I’m not sure how many yet. Need to do my final counts. I should have some populated TXHelper boards left that aren’t paired with a Teensy 3.6. Not sure how many or what I’m going to do with them as I’m about as sick of soldering Teensy headers as anyone could be at this moment and just can’t go there yet.
Just for clarity, I should point out that the TXo and TXo+ have exactly the same functionality. You only should want/need/desire/covet/lust-for/dream-about an upgrade if you are frequently using your TXo as an oscillator. A TXo+ allows for a) a slightly higher sampling rate, b) less aliasing on the basic primitive waveforms (sine, triangle, saw, and square), c) less aliasing when combining features with oscillation (like pitch slew or envelopes), and d) a gaggle of additional waveforms for the oscillators. The unit will still need additional external filtration in order to be the best oscillator that it can be (4-pole instead of 1-pole).