Thread Live Monitoring w/ Two Pro 40s in Dual Unit Mode

I was hoping that somebody might be able to help me figure out why I can’t get my two Saffire Pro 40s to work correctly in dual unit mode. Both interfaces work perfectly individually, but when I try to connect them, I can only hear the instruments/microphones coming out of whichever Pro 40 my headphones are plugged into. I would like to live monitor audio from both interfaces at the same time.

Just to give you an idea of what I’m trying to accomplish, here’s what I’m aiming for: I’m in a 6-person band (drums, percussion, keyboards, bass, and two guitars). We use a PA during practices, but we’re in a rather small room and I’ve had significant difficulties with feedback (I play drums and sing, so whenever my monitors are loud enough for me to hear my voice, they begin to feedback). My goal is to be able to mic every instrument, including my drums, and run two mixes out of my Pro 40s: one mix for the PA (without the drums, to avoid feedback), and another mix for my headphones (with the drums, so that I can hear them while I’m wearing my in-ear monitors). Using this setup, I also hope to be able to make halfway decent recordings of all of our live practices through Logic.

Here’s how I have things set up:

- Pro 40 #1:
- Inputs:
1. Left Overhead (Drums)
2. Right Overhead (Drums)
3. Hi Hat
4. Snare Top Mic
5. Snare Bottom Mic
6. Kick Drum
7. Percussion
8. Bass

- This interface is connected directly to my computer (a Mac) via firewire (firewire port 1, on the interface), as well as connected to the second interface (firewire port 2)
- I have a S/PDIF cable running from the S/PDIF OUT of this interface to the IN of the second interface

- Pro 40 #2:
- Inputs:
1. Vocals 1
2. Vocals 2
3. Vocals 3
4. Vocals 4
5. Guitar 1
6. Guitar 2
7. Keys Left
8. Keys Right

- This interface is NOT connected directly to the computer; it’s connected to the first interface via firewire
- As with the first interface, there is a S/PDIF cable connected from the OUT of the second interface to the IN of the first

- As per the Dual Unit Mode instructions, I have two mixes made for each interface – one to route through the interface’s line outs, another to run through the S/PDIF to the other interface.

When I plug our PA into the live outs of interface #1, I can only hear the instruments plugged into that interface (same with when I plug my headphones in). When I try plugging the PA and/or headphones into interface #2, the same thing happens. I believe that the problem is with the S/PDIF signal. When I assign S/PDIF input from interface #2 to a stereo channel in interface #1’s mix in MixControl, I hear no audio coming through the channel. I’ve also tried running ADAT cables to and from each interface, just for the hell of it. That hasn’t worked either.

I’m sure that I’m most likely missing something obvious, but this is driving me crazy. If anyone could offer some insight, I would be very appreciative. (And PLEASE don’t tell me to read the Pro 40 or Dual Unit Mode manuals – I’ve read both of them a dozen times, and precisely followed every instruction.)

Thanks in advance for the help.

Will