Although it is not possible to create a single monitor mix from multiple Saffire PROs solely using the Firewire connections (as the Saffire range's latency-free monitoring is achieved by internal routing), there are other ways to create the same effect. One possible solution is detailed below:
If you create the desired monitor mix for the channels on the Saffire PRO not connected to your speakers (which I will now refer to as Saffire PRO 2), you can route this mix to the SPDIF outputs (9/10), making sure that outputs 9/10 are only monitoring the input mix, as shown below:
You can then connect the SPDIF output on Saffire PRO 2 to the SPDIF input on the Saffire PRO connected to your speakers (from now on, Saffire PRO 1).
Having created half of your monitor mix on Saffire PRO 2 and sent it to Saffire PRO 1, you can then create the second half of your monitor mix on Saffire PRO 1 and route the whole thing to your monitors. As it is possible to switch between units easily in Saffire Control PRO, it is simple to make adjustments to both halves of the monitor mix, as shown below:
The only downside is that you use 2 channels of SPDIF to achieve this, however if you need all 4 channels of SPDIF, you can always achieve this using analogue or ADAT inputs/outputs instead. I have only described it in this way as the SPDIF inputs/outputs are more likely to be available than the analogue and ADAT inputs/outputs.
PC Users: Before using multiple Saffire PROs simultaneously, please download and read the Saffire PRO26 User Guide Addendum, found here, with particular reference to the section entitled ‘ How to use multiple units with a PC’.