Add second SFX stream

[sikthehedgehog]

To prevent SFXs from cutting each other. This may mean Echo will need to learn to allocate channels, since now you can't hardcode them anymore if you want any two SFXs to play at any given time.

[Mikejmoffitt]

+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1+1

[marcb0t]

Very interesting idea.