No Freeview receiver incorporates DAB radio. But they all give radio channels.
Yes any receiver can be connected to the AUX input of an audio system, either direct via phono sockets, if it has them, or via a Scart -to - phono adapter.
Cheaper boxes tend to be less reliable in my experience.
I have done a Google search for you as I knew nothing about "Audio description". I found a page which describes it and has useful links for more information. Here's the link:
http://www.bbc.co.uk/ouch/closeup/au..._guideto.shtml
Here's the important paragraph:
"The Netgem iPlayer TV set-top box, at the time of writing, costs approximately £100 + delivery. It is the only Freeview box available that can receive Audio Description. The box also allows you to hook up to the internet and have TV guides spoken to you. Plus, you can adjust the Audio Description volume separately from the programme sound - a feature considered useful to those with hearing difficulties.
Call 0800 0153092 to purchase an iPlayer."
I don't know if this information is up to date of course. You might like to contact the RNIB whose phone number and email address are on that web page, just below the paragraph which I've quoted.
I hope this helps.
Sam.