Hello there. I think I've added the feature you requested before; please download the latest build and change the plugin parameter to the folder you want to use. (Make sure to put the new folder into the audio folder and your SEs inside it.)
For the second request, it would actually be a lot of work, and I would much rather focus my time on releasing more plugins for the community. I'm sorry about that.
However, I know what I would do in your situation. I would just use the ME folder as the new voices folder, and it will automatically make it compatible with the VisuStella Options Core and allow the sound effects and voice sound effects to have unique operating volumes. Just change the name of ME in the options menu to "Battle Voices" or whatever you want, and the player would have no idea and it would be functional and serve its purpose. I mostly never use the MEs because the SEs work the same way and serve no real beneficial purpose for most games. You can even play MEs from the SE folder. I hope this helps, and I would like to give you my thanks for supporting my plugins.