Be careful with your use of ESMs.
BSAs are just what their name implies, archives. They contain resource files like NIFs, DDSs, sound files and whatever, and are used instead of distributing loose files with your mods.
They will not, however, "add files to the Data folder" when activated, as this is against their intended use concept.
The game uses the resources from within these files right out of them. If anything's 'extracted', then only inside some kind of 'temporary' folder, and it will be removed again as soon as the game's closed. Though I'm not sure there even 'is' anything extracted at all to begin with. You will never find resources from inside a BSA lying around somewhere in your Data folder while playing the game or anything.
ESMs now are something completely different, and also quite unrelated even. An ESM is a Master File, that is the same as a Plugin but its records are meant to be overridden by the same records used inside other ESPs. That's how modding the base game even works to begin with. The game uses all records from within the original ESM and overrides them with the same records when found in ESPs loading later. And ESPs are always loading later than ESMs for that reason.
An ESM cannot, however, be used to introduce a record into the game that already exists in the base game ESM(s). Only 'new' records can be introduced through an ESM. That's why not everything from inside an ESP can be converted into an ESM without causing issues later on. ESPs will always override ESMs' records, but the same is not guaranteed for another ESM. An ESM, basically (the actual results are random and unreliable in fact), cannot override records from another ESM or the base game, and, of course, will also always loose against an ESP doing the same.
So in short, I'm not exactly sure what you intend to achieve by converting your totally fine ESP into an ESM here. But chances are it isn't doing what you think it does.
Second point, and likely far more relevant to your topic though, is the folder naming convention for voice files and such. If I recall correctly, they are found inside a folder named after the ESP or ESM which uses them, and if I'm not mistaken, the folder name even contains the "suffix" as well. So chances are, if you change your ESP into an ESM, but the voice files are still inside a folder named "MyCoolMod.esp", this will not work out for the very simple reason that "MyCoolMod.esp" is now actually "MyCoolMod.esm" instead.
(And my usual disclaimer:
This is all deduced knowledge from Oblivion modding, only brought up because the GameBryo games actually haven't changed much in most regards ever since and what I know from Oblivion in many cases still applies to all the others as well. So take it with a reasonable amount of doubt and as a pointer rather than an answer, and wait for others more knowledgeable than me in this specific regard to chime in first before taking anything told to you for granted.)