[anpaza]

The transcoded AC3 bitrate is always 384 kbits? I've read that was limited due to bugs in some weird sony TVs?

Yes (on Android only: 640 kbit/s on all other OS including 25$ RPi). AC3 is lossy anyways. It makes zero sense to reencode a decoded signal back to AC3 just to see Dolby on the AVR display. But for those shitty boxes with just ARC output there is no alternative as they are limited to 2 PCM channels.

Wouldn't it make sense to make that a user setting? E.g. instead of a ON/OFF switch, just let the user pick one of "disabled", "384 kbits/s", "448 kbits/s", "640 kbits/s".
I use the optical S/PDIF to connect to my AVR and, as far as I understand, that does not support LPCM, only HDMI supports it, right?
My AVR is 10-year old and doesn't have HDMI in, so without re-encoding to AC3 I would be always limited to stereo.
But I don't see why I should enjoy 384kbit/s just because some existing device doesn't support 640.
Letting the user choose it would allow to balance between various limits, not only sony tvs but cpu load, firmware quirks etc...

By the way, I think the datalink speed limit of 48kHz/16 bit stereo is 1536 kbits/s? Why not use this bitrate, am I missing something?