Have you tried citrus wood cleaner or Liquid Gold wood polish* that has always worked for me. One thing you can do to prevent future marks is remove the rubber feet and wrap them in saran wrap tightly and re-install them. It won't affect bass, mid or treble but will keep the wood clean. We all want clean wood.
* also murphys wood soap, fantastic, 409, pledge to name a few more you might have a round the house. If by chance these don't and the stain remains, the finish on the wood has been comprimised and you may have to refinish. One last ditch effort before refinishing is steel wool but that will dull it some. But if the finish is that thin you may not notice.
* also murphys wood soap, fantastic, 409, pledge to name a few more you might have a round the house. If by chance these don't and the stain remains, the finish on the wood has been comprimised and you may have to refinish. One last ditch effort before refinishing is steel wool but that will dull it some. But if the finish is that thin you may not notice.