Can anyone confirm that the Vega G1 does or does not support the iTunes m4a format?
In what manner? When used as an USB DAC or as a streamer via UPnP?
As an USB DAC it’s up to the host to transcode the stream into a usable format, so yes, if your computer/software can use it.
And with UpNp server you likely can configure the server to transcode into a PCM stream to suit the Vega.
It does very well.