Recent Radio Downloads Not Playing

[Budge]

As will be seen from earlier thread I have been having trouble with my 
Linn DS devices which cannot cope with large m4a radio download files 
with sound encoded as AAC.  These files were generally over 300 MiB and 
about 2 hours playing time.

Over the last weekend I tried to play the News Quiz Extra which is shown 
as about 45 minutes playing time and it would not play.  Last night the 
even shorter "The News Quiz" would not play.

I wondered if it was an issue with some cache in Linn not being flushed 
so rebooted and tried again with new and old downloads of latest "The 
News Quiz" but still no joy.  Last week's programme does play.

This suggests to me that there may be some differences between the radio 
downloads over the last week or so ago and those earlier.

Could this be so and what are the changes?

Finally I see that the radio downloads are defaulting to dashhigh. I 
really do not need this for spoken material.  Is there a 
thread/link/wiki where I can learn what prefs I should now set for audio.

I will keep the best for music and opera &c on the Third Programme so I 
may need help setting up GiP to discriminate if possible.