You can purchase piano cleaner fluid, and use a microfiber cloth or similar (e.g. piano cleaning cloths).
How To Clean Piano Black Speaker Finish?
What do you use to clean your speakers Piano black finish? I am using a slightly damp microfiber cloth. So far, in 2 years, no scratches. Is there an easier way to keep them clean? I have used a very clean wool duster a couple of times but it doesn't help fingerprints like when I move them. Anyone?