According to
www.joinfreesat.co.uk forums, loads of people have bought them (now sold out everywhere it seems), but the earliest delivery date is tomorrow (24th), so I think it maybe a day or two before you can get a definite answer to your question and even then, it will require someone with an existing dish as I doubt anyone got dish installation as a package so quickly.
That said re-reading I'm a little confused. It won't be able to record HD sound because as far as I know HD broadcasts aren't broadcast in HD sound as it takes too much bandwidth. I understand HD broadcasts are Dolby Digital 5.1 instead of Pro Logic on analogue, but I stand to be corrected on that. If you're asking does it have the potential to record HD sound for the future, I simply don't know but maybe the WHF team will after their tests.
Alternatively, did you mean to ask can it record DD 5.1 in SD?