To start, be sure your snake system or V-Mixing system is sending adequate audio signals. (If you are sending direct out's from the M-400, are they pre-fader? If you sending AUX SENDS, are they turned up? etc). Try connecting a powered monitor to a REAC B Output port to verify you are getting audio from that port. Once you're sure your REAC B Output ports are producing audio, you need to make sure your M-400 console and RSS Digital Snake devices are all fully updated with the latest firmware or patches. The M-400 can be updated via USB stick, but the Digital Snake devices must be updated using the S-4000RCS program and a 9-pin serial connection. Visit our downloads page to get the latest: www.rssamerica/downloads.