Now that Apple users are using a semi emulator, will all these various music plug ins work for us?
I would think they should. I have been using Crossover for sometime with success and all my plugins function normally. Remember, you are now running the Windows version of the game, so anything that works there should work on a Mac.
If you hunt through the Mac Technical Support forum, a couple of folks whom I've helped have mentioned that they use the mod Songbook. As I understand it, Songbook is both a mod and has a companion application. I recall one person telling me they installed the Songbook application into the same bottle they use for LOTRO and it works well. Other music mods should also work – any mod that works on a Windows box will work on a Mac running either the "Mac"/WINE client or the Windows client in Crossover, some Windows applications might not work but most should and I haven't yet heard anyone complaining about a LOTRO mod's companion application failing to work in Crossover.