I have a Humax Freesat box (now retired for the Quad Plus) which did DD 5.1 over S/PDIF or HDMI from sat. The Quad Plus also does this as does the MB. I haven't come across AAC audio on broadcast yet. The Irish Freeview system is only using MPEG-2 audio at the moment although the specs for any boxes used on the system require AAC support. I presume they will turn that on at some stage when they start experimenting with surround audio, but it's not available yet.

I wasn't actually aware that Freeview HD was using AAC. I presumed it was DD (or AC3 to be more correct) like Freesat. In which case you wouldn't have an issue with S/PDIF!

The MB may well decode DD or AAC to six channel PCM over HDMI, but I'd have to swap around the boxes to check but can't do so at the moment - sorry!