Multichannel expansion

# Use set notation?

``` clojure
#{c e g}
```

Can ordering be relied upon for small collections? Would relying on that be inelegant?

``` clojure
(p/bind {:degree [#{0 2 4} 0 1 2 #{1 3 5} 1 2 3]
         :amp    [#{1/4 1/2} 1/4 1/4 1/4]})
```

Should sets be unpacked during, prior to, or after `bind`ing?

Handling during `play` seems ugly? Perhaps Breaks with data focus of library?
