Hi Fi World (sorry Claire, Andrew, Andy, etc...) do free classifieds, so you can put your speakers on there at no cost, plus enough word space to put in a reasonable description.
Ebay will hit you for a listing fee, a selling fee and, as PayPal is mandatory with many people paying through that, the money handling fee too. Double dipping by Ebay (as they own PayPal) but I'd look to the free classified sections first. You are at least pitching to a fairly knowledgeable market and can set your price or o.n.o.