Headset Services at Shoreham airport should be able to let you test their stock, with a suitable noise source in the background.
I warn you however - when you have done this there is only one headset which you will walk out with: the Bose X.
Still, in flying there isn't a lot of stuff to buy. You need a decent headset (£800), a decent GPS (say £1100 for the Avmap EKP IV) and that's about it, and provided you don't lend it out it will last you many years. All the junk used in training can go on Ebay.