Woodworkers ?

Depending on the depth of the scratch and the thickness of the veneer. First rule of thumb, less is more in such matters. I would try a very fine grit sand paper (no less than 220, depending on the depth of the scratch) and use a soft rubber backed block or the palm of your hand, DO NOT use your fingers and focus on just the scratch other wise when you refinish it will be noticable. Let the paper do the work and be gentle and always sand with the grain, always gently. To get the sheen back use progressively finer grits of paper and 0000 steel wool. Talk to the manufacturer about the finish and stain (if any) used. I would imagine lacquer is what most use, faster and less labor intensive, although some may use an oil finish.

If in doubt about the above, leave it alone or let a professional look at it.

If you are just trying to mask the scratches, rather than remove them, a little English Leather in the right tone works quite well. It won't give the professional results that Tubegroover's method will, but you run little risk of hurting your speaker.

You may want to try colored lemon oil -- this product does not remove the scrath, just covers with colored oil to make it less visible.

The MFR may have some suggestions or products available for this purpose.

There are other products such as colored fillers that may work as well.

Since you are asking others for advise, I would assume that wood finish repair is not your specialty. With that in mind, I would avoid the use of abrasives at all costs. Some speaker manufacturers use tinted lacquer for a coating, and as you sand, you may remove layers of color, hence changing the look of the entire area that has been sanded. If you choose to use abrasives, I would use 600 grit wet sand or higher. The all advise in the above post is also good, with the exception that I do not agree with 220 grit -- to rough in my opinion.

Keep in mind you are probably working with 1/16 or less of veneer thickness. You remove too much you will have MDF visible...

Good Luck