Couldn't see anything, but I've sussed it out now.
After trawling the web ...
AVLS = Sony's proprietary AVLS volume adjustment technology
Basically if you turn it off, you can increase the volume, however it looks like distortion can creep in etc. I guess if you have it on it manages how loud you can go without distortion etc.
In my vew though, with it turned on, the Max volume is way low.
Depends whether you're on a noisy train or a in a quiet park.
