I bought some Harman Kardon Soundsticks from the apple store online which are faulty, how do I return them?

I bought some Harman Kardon Soundsticks from the online Apple Store, which keep 'going to sleep', and the only way to restart them is unplug them and plug them back in again. Harman Kardon say this suggests they are faulty and that Apple (as the retailer) should replace them. I can't find any way to open this as a case with apple online, can anyone advise me? (I've found how to contact Apple about Apple products, but not third party equipment sold through the store...) Thanks