I know, you’ve been on tenterhooks: did I ever solve my wireless headphone purchasing dilemma? Yes! I did!
In the end I picked up a pair of Philips phones – no idea what model number – from ASDA, which set me back about £20. And they’re fine. The trick is to turn the audio source up very loud and the headphones fairly quiet, and that way you get nice clear sound without hiss or other audio artefacts. I don’t seem to be getting any interference from the wi-fi or from anything else, which is nice.
On the downside, playing the Berserker bit of Gears of War is utterly terrifying on headphones.