Re: MintDice – Bitcoin Casino With Online Slots, Bitcoin Crash & Bitcoin Investment
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.