On your first question the answer is no, i havent tried it in the browser yet because im building for iphone.
So i dont need to test in the browser anymore.
On your second question the answer is also no.
I have tried to set the volume directly in the "playsound" action with and without a tag.
It plays the sound correctly at the minus volume, but all other sounds also drop in volume with it.
And that is with or without their own tags.
It appears that atleast on CocoonJs all sounds are now volume linked.
So they need to become individual again.
Normaly thats what the "tag" is for.
Ps: Yes the new volume option is a gift the scirra team has brought us.
It just needs a tiny bit of finetuning to make it realy perfect.