I've probably said this before, but you are my hero! I'm reminded of the film 'Wayne's World', the original, not the sequel (it's just better)... On meeting Alice Cooper (or was it Aerosmith?), Wayne and Garth fall to their knees in supplication and start chanting... "We're not worthy!"
In this instance, you are Alice Cooper (or maybe Steven Tyler), and I'm probably Garth. This drivel will mean nothing if you haven't seen the film!
Saving the BSA uncompressed did the trick. No CTD! At least it did using wav files. No reason to assume that it won't work using xwm format... Another test coming up, I think. If that's fine, then I want to see what difference there is in filesize compressed v uncompressed. I may then choose to have 3 BSA files, one for textures, one for music and one for everything else. Neither 'Beyond Skyrim' nor 'Project AHO' does this with their BSAs, but that's not to say that what they do is right! If compression is only useful for textures, then that would explain Beyond Skyrim and Project AHO lumping their music tracks in with the meshes, SEQ, etc.
BTW, for anyone reading this, when you try to get an xwm format music track into the game, you aren't allowed to add any track except if it's in .wav format. The way around this is to make your new 'Music Track' form in CK, click 'Choose File' and then start typing the name in the 'File Name' field at the bottom of the dialog box that opens. If you don't do that, your xwm files won't show up and the dropdown menu for formats only gives you the option of .wav. As soon as you start typing the filename, a box appears under this field with all the available options. Choose your xwm file and OK.
The Wiki gives wrong advice on this, telling you to use a wildcard search in the wrong place. I tried it. It doesn't work. My method does work.
Edit: it works for xwm files, too! Now I just need to see about separating the music BSA from the meshes etc. If that leads to a more compact upload file, I'll do it. The problem there is that I know about adding separate 'textures' BSA files, but not music. I believe that not compressing that BSA has increased it from 40 MB to 54 MB, using xwm music. With WAV files it was over 100 MB. That suggests that there is some compression going on in the other files. I may be able to restore that and get the BSA much closer to 40 MB. This may not seem like much, but if my mod was 10x bigger, I'd be saving 140 MB from the player's HDD. I'm probably verging on OCD about this, but I hate unneccessarily large files!