I'm almost sure your speakers are finished with a 2 Pack sealer and clear over a spirit stained veneer. After preparation, satin black 2 pack can be sprayed over the original clear coat, a sealer shouldn't be necessary. 2 Pack is nasty and should be applied in a spray booth, so a good well equipped spray painter can do the job. I did a quick search and it looks like your speakers were sold in black also. Popularity of solid or clear finishes may determine resale value. I hope this helps.
