I've been using https://github.com/Jalle19/node-ffmpeg-mpegts-proxy with a number of UK Radio AAC Streams (and NASA TV amongst others) and it's been working well.
As for the XML Grabbers, I've not used the internal ones as the UK OTA EPGs are rather comprehensive, however I belive the steps are as follows
(The following tv_grab_### name can be found under the path of tvheadend's Internal grabbers configuration page)
SSH into the server running TV Headend
sudo su -l hts
/usr/bin/tv_grab_pt_meo --configure
follow the steps shown on screen.