As a few people mentioned above, some types of veneer can be refinished if one is very careful. These veneers are usually used on furniture meant to withstand daily contact (like an armoir or dresser) and are MUCH thicker than those typically used on speaker cabinets which are usually only slightly thicker than a childrens colored contstruction paper. Unfortunately for your situation, it is highly unlikely that you have a refinishable veneer, unless these are VERY expensive speakers.
However, Prpixel has a good idea and probably the only workable option mentioned in this thread (other than reselling the speakers and buying the ones with the finish you want). Having them vacuum veneered is the proper (and best) way to do the job to insure good veneer adhesion, but if you are fairly handy you could attempt a re-veneer yourself to keep the cost down. All you would need is the veneer, adhesive, several sharp blades, a good smooth roller and plenty of time. Be careful and take your time...that is the key. Keep in mind, though, that trimming veneer can be a real PITA. Hope that helps and good luck.
However, Prpixel has a good idea and probably the only workable option mentioned in this thread (other than reselling the speakers and buying the ones with the finish you want). Having them vacuum veneered is the proper (and best) way to do the job to insure good veneer adhesion, but if you are fairly handy you could attempt a re-veneer yourself to keep the cost down. All you would need is the veneer, adhesive, several sharp blades, a good smooth roller and plenty of time. Be careful and take your time...that is the key. Keep in mind, though, that trimming veneer can be a real PITA. Hope that helps and good luck.