We do support multiple containers, and it is reasonably abstracted (but it is slightly leaky right now).

The support for multiple streams isn't there yet, it is something I would love to do, but it is reasonably complex and I have been researching about how to best support it, but I am not really sure what models works best in a browser.

If you want to add some input about it, I would love to hear it. (#ofmlabs on freenode, or send me an email)

Ps. We managed to get Typed Arrays to work with JSMad, so that stuff is in now.