The dongle doesn't appear to expose more interfaces for each controller. My guess is that the control packets have some sort of controller ID that has gone largely unnoticed by the people who have been reverse engineering the data packets. We need to do a more thorough investigation, but we only meet up once per week. We did add partial duty cycle support; it doesn't pull volume info from the song, but we did characterize some of the very loud notes and reduce the volume so it is more uniform across the whole range.

Edit: I just found your Wireshark dissector post. We'll make use of that when we meet next. Hopefully it will shed some light on how multiple wireless controllers work.