I've noticed that the 320kbps audio streams that used to be default for hvfhd/hvfsd/hvfxsd TV seem to have disappeared and have been replaced with 128kbps streams.
Looking at my series downloads the change appears to have happened around 3rd week in June, for instance Episode 4 of the 'The Planets' downloaded on 19th June has 320kbps stream, Episode 5 downloaded on 1st July has 128kbps stream.
As far as I can tell all current programmes now only have the 128kbps stream available (I noticed this because Glastonbury downloads were all 128kbps).

I suspect this a BBC change and there will be nothing that can be done in get_iplayer to re-enable 320kbps (but I hope I'm wrong!).

Nothing get_iplayer can do about it. If anyone can amend get_iplayer so that it can access 320k audio TV streams that it cannot currently access, feel free to submit a pull request. Thread closed.