I just wanted to chime in on this topic, I am a wood finisher by trade and would like to offer some advice. First off if your speakers only have minor blem's ( surface scratches, small chips) there is a great product called Briewax, it is a pigmented wax (which comes in ebony) it is applied the same way a car wax is and build's up as multiple coats are applied. Home depot used to carry it, not sure anymore but alot of antique furniture stores sell it.
Next if damage is more significant ( crushed corners, deep scratches) fill with wood filler, bondo works great to build up damaged corners. If you are good with a paint brush, Minwax makes a product called Polyshades, it is a colored polyurethare, comes in black, clean cabinets good, lightly sand and apply with good quality brush, or roller. If you use a roller I recomed using a mohair roller and apply multiple thin coats sanding in between. The best method is to do all necessary repairs and apply a black lacquer paint with a spray gun, just did my L1's and 5's any they look awsome. I know this is not something everyone is capable of, but if you find a local cabinet shop or refinisher they may be willing to do this for you. Hope this helps