I'm not sure I would want to listen to music through my Scala, because the Scala doesn't cut down on wind noise, so if I'm travelling at speed, then I would have to turn up the music to hear the music better - I like fuller sound. I've never listened to music through my Scala so I'm just guessing - no experience with it. If I'm wearing earplugs for a long ride, then I might as well be wearing earbuds that play music....
That said, I listen music often when I ride. Not when in the city and running errands and stuff, but when I go out on longer rides. I prefer to use very small noise isolating in-ear speakers that also double as earplugs even when music isn't playing. I can hear sirens and vehicles around me, but they really cut down on the wind noise. I also use a Scala and I can hear the person I'm talking to quite well, as I keep the music at a pretty low volume..
The ones I have most recently used are the Etymotic brand. I am currently using a pair of the ER-6i's and ER-6's. They are really small and are easy to put my helmet on and off without getting snagged by the helmet. They have excellent sound quality for what I'm looking for. They are so small, that after a while it doesn't even feel like I'm wearing them and they still allow me to hear the world around me.