SoundCloud has always had the low volume issue. It will be fixed in the 0.5.0.0 update. As for the YouTube issues, Valve updated the Steam web browser and it seems to crash on advertisements or just randomly. We use the Steam web browser for our media player, which is why it has issues.
We are currently working on a fix, however, we can't immediately put a patch out as we have 0.5.0.0 being prepared.