I checked the database at "fmstream.org" and it lists a 128kbps/mp3 stream and a 48kbps/aacHE stream for BOTH BBC Radio 3 and BBC Radio 6.
The aac stream for BBC 6 is: "
https://a.files.bbci.co.uk/media/live/manifesto/audio/simulcast/dash/nonuk/
dash_low/aks/bbc_6music.mpd"
and the aac stream for BBC 3 is: "
https://a.files.bbci.co.uk/media/live/manifesto/audio/simulcast/dash/nonuk/
dash_low/aks/bbc_radio_three.mpd"
48kbps/aacHE isn't high def, but is certainly listenable (I would choose that any day over a 128k mp3 stream). Both aac streams work in my Windows browser, as well as on the player apps installed on my android phone. (I did not try them yet on WiiM, but I have never had a stream not work on WiiM that plays on my androids). Interestingly, the 128k mp3 streams listed on fmstream.org are both dead... note sure if these are the discontinued Shoutcast streams referenced earlier by d6jg