Ok, I found a way to mute or swap voice-overs. I'll write it here for reference, since there's little info on this subject.
1) To identify the desired audio line, it's better to view the soundwave asset in Frosty, since it shows the subtitles for each stream. In the right panel, search for the correct stream under "Segments", and annotate the number next to "Sample offset".
2) Convert this number from decimal to hexadecimal.
3) In DAI Mod Maker, export the EBX of the soundwave asset. Open the exported EBX in a hex editor, and search for the hex number (in little endian, that is, reversed)
4) Change the original number to FF FF FF FF (to mute the line), or to the hex value of a different line (to swap voice-over). Save, and import EBX into DAI Mod Maker.
This may seem a bit convoluted, and it's probably possible to edit the sample offset in Frosty. But I've had no luck loading mods with that mod manager, so this is the way I've found. Also, trying to edit the EBX directly in Mod Maker, mutes the whole conversation.