In my opinion, how if there is a notification message while opening the game? Message which ask players whether they want to enable/disable sound or not on the game. If it is a bit complicated to add then giving an option to disable and enable the sound is enough like what we usually see in most other gambling sites.
From usability-perspectives I would prefer this solution, too. But it is way harder to implement than switching the sounds off per default
Anyways, I would prefer an opt-in for new features, meaning that a user has to explicitly turn on sounds if he/she wants to have them. For existing features I wouldnt touch the default settings, otherwise you may get complains that something isnt working what was already working before.
If we are going to give feedbacks on anything I know website is going through a whole change so might as well put it out there; I think adding new games could be life changing for the website, notification sounds should definitely be disabled as default and maybe disable the "music" thing as well because notification sound is not that bad but the music is really ... not needed? I mean is there a reason to have "music" in a casino?
I feel like we can pick our own songs to listen if we want to from like spotify while we gamble. So the only thing would be removing the music part and adding newer games if I had to give a feedback, that looks like the only things I can think of, we all know there is already an overhaul process going on so maybe we can give better feedbacks after that.