sky+ outputs dolby surround or Pro Logic from those programs or films recorded using this method. This system on your link has Dolby Prologic II which enhances these formats and takes the sound closer to Dolby Digital.
Even better, Sky Movies 1,2 and 3 have Dolby Digital 5.1 (on some, not all) films. To get at this your receiver must have an optical digital input.
Looking at the spec for this sytem, it mentions optical connections so it sounds OK but you need to confirm that these can accept the output from Sky+.
The Sky+ has an optical out and, if your intended receiver has an optical in, which it would appear to have according to Leander, then you will definitely be able to access the Dolby Digital 5.1 from Sky Movies 1, 2 and 3.