I think I still need to do some more thorough testing to determine if it's worth keeping in there, but some of the newer UAs have switchable MOSFET input/output buffers. Nobody has had any impedance matching issues with UA, but it came up every now and then with PAX so I thought I would experiment with using high-voltage MOSFETs for buffers. There are a couple LND150 you can see in there on the right side (Q3 and Q4), I like them because I can run them on the same 235V rail as the tube.
Initial tests showed that they work fine, but I've had one person try them out and they didn't. So I haven't documented them on the website or written up any usage guide on them yet, I want to do some more thorough testing and if they work consistently (again, shooting for 100% reliability) I'll keep them in and put some instructions online, if not I'll pull them out. Either way the DIP switches allow them to be completely bypassed, so they do not impact the circuit at all when not in use.