hmm, strange!
i have an emu xboard 49. but even when thats not plugged in its mutted.
i also keep getting a pop up window informing theres a midi problem and it tells me to reset midi drives, through the preference window, which i do but the problem stilll persists.
very strange that it works fine your side though!
so your getting sound coming out of strip 1,2 and 3?
i would just delete this project and start again but this problem happened to me before and im sure it will happen again so there must a cause!
cheers