I've only really zoomed through the thread, so you'll have to forgive me if I have missed some pertinent details. I thought I'd just chime in regarding the teaching aspect: As yet, I've never needed an additional 'bass preamp' before my interface. However, if I felt the urge I do have a few on my "shelves of pleasure". I just made that up, on reflection it sounds way more dodgy that it's supposed to. I digress. A decent interface with a higher enough inout inpedeance isnt really that different from the input of a "transparent" bass preamplifer. So, rather than worry about getting my tone with extra boxes, I have always shaped the sound with a really good plugin. My teaching favourite for absolute clean (and totally dry) to mildly driven sounds is the Neural DSP Cory Wong X - in the DI/Channel strip setting. No amp sim, no cabinet. It is bonkers good when you get it dialled in and I'd highly recommend that over messing about with additional hardware. *unless the interface being used can not accomodate the output needs of the instrument. (Which I am yet to find on anything with more than two inputs). Just a thought!
Oh, if you're on a Mac and you are using OBS or similar for online lessons you'll have no doubt come up against the issue of getting "computer audio (plugins/DAW/usic palyer) and microphone out to the other party" and this is also fixable.