Sequences are independent of each other. Simply drop the master audio file into each Sequence. It's pretty easy. As long as each Sequence has the same video frame rate and audio sample rate settings, just drop that one audio file into each Sequence. Export each sequence as a QT file. Done.
Otherwise, I'd just do video without audio, and sync each of the 7 monitors to the same audio playback source, and have that play your master audio file. That has nothing to do with FCP 7 sequences. That's just a hardware configuration issue between the monitors and some audio playback device.