Ok! I've fixed the first Magedom conversation!
To do it, I inserted extra 3-byte buffers (I used 00 00 00, which makes people 'say' the beginning themesong so I can easily tell what I'm fiddling with, but later I'll change it to copying something nearby so they repeat themselves). I inserted these buffers at 134C, two of them (six bytes total) at 1364, one at 138B, and one at 13E5. They possibly could be moved a bit in one direction or the other (I don't know Japanese, so I don't know how it's precisely supposed to line up), but this works well enough.
Additionally, as I mentioned in my previous post, I deleted other things, because moving too much breaks sound entirely (I'll bet there's something defining the size of the whole table that can be changed to avoid this, but I don't know how -- this will do until someone who knows more can fix it.) Instead, I just deleted bytes around 4270, where there's a long string of repeated "A2 00 E6" pointers -- hopefully those are dummies for unused sounds or something. I just deleted one "A2 00 E6" for each "00 00 00" I inserted earlier, which moved all sounds forwards by the correct amount.
I'm going to play a bit more... I assume, from what people have said, that it desyncs again on a later conversation.