The standard cherry vinyl is very resilient. If a guest uses a tower speaker for a coaster (it happens, I know) you can remove a ring with a damp cloth and it won't hurt the speaker finish at all. The real-wood finish is similarly tough - but mustard will stain it if you leave it on overnight. I'm not sure what circumstances would lead to that, but it was a warning in the product literature!

For general day-to-day care, the other suggestions are perfect - microfibre cloth or a vacuum with a duster attachment on it.