Just go to home depot and look for contact paper or vinyl from there.
As far as gloss paint...if your not good at a smooth finish, it can look bad really easily. The hard part is getting the final clearcoat to be smooth and consisent throughout the entire speaker. There are ways to work around it, but it's all up to how many hours you want to spend on your paint. To me vinyl or contact paper would be a better answer.
...or jsut go all out and get some veneer, but that stuff has it's own tricks to making it look right, and is rather fragile since it is super-thin wood.
BTW if you have teh sealed 12" KLH speakers that sold in best buy around 2000...I forgot the model name...consider internally bracing the cabinets, I found that some of the cabinets on that model were prone to having the front panel break loose if you play bass-heavy music at a high volume. After bracing, that pair took some hardcore abuse.
