Try not to push any goo further into the holes. Before the peanut butter dries, try using a vacuum cleaner to empty the holes, then use a detergent dampened rag to remove surface deposits. You’ll probably then need another session with the vacuum cleaner. I’d want to work with the grill facing down in order to discourage anything from migrating to the speakers. You may need to find a small round shaft to poke open some holes. Do this after the vacuum cleaner attack and before the peanut butter dries.

From Sonos:

Clean only with dry soft cloth. Household cleaners or solvents can damage the finish on your Sonos components.

Thanks buzz, grill facing down is a good idea

Sellotape/sticky tape. Gently lay it on the grill so you don’t press it in further and the peel off.   This is what I did on my Move that had cake mixture on it!!  This got most of it, last few stubborn bits required puckering up and sucking. Vacuum probably would have worked as well but I didn’t think of that.