I would get a couple pieces of walnut at you local lumber yard or woodworking supply store and test a few stains before even touching the speakers. The veneer on the speakers is probably thin and won't permit much sanding.
If you can't get good results with the sample pieces you will have to re-veneer the speakers with rosenut or a wood tha can be stained to match the color/effect you seek.
But the re-veering may change the cabinet dynamics of the speakers.
If you can't get good results with the sample pieces you will have to re-veneer the speakers with rosenut or a wood tha can be stained to match the color/effect you seek.
But the re-veering may change the cabinet dynamics of the speakers.