I have a Pro 24 DSP (which incorporates the VRM functionality) and bought a Pro 40 to increase my input/output options.
I have followed the "dual-unit" instructions to daisy-chain them together via Firewire and linked them via S/PDIF I/Os.
(I got a bit confused here because the example in the instructions uses two Pro 40s.)
The Pro 24 DSP has a single Firewire connection, the Pro 40 has two.
The Pro 40 is plugged into power; the Pro 24 DSP is not but takes power through the Pro 40 connection.
The I/Os for both units are listed in Preferences and I select all except the ADAT and Loop options.
I get to the point where I can use the interface for tracking and mixing but I can't get any sound through the VRM.
Anyone any ideas? Thanks.

Hi Guylemec,

Sorry to hear you are having a hard time getting the dual unit mode going.   Since there are some settings that can make or break this setup in MixControl, I think the best way to help you will be for you to submit a support request at focusrite.com. When you do so, make sure you include a screenshot of the MixControl window for each unit.  This way we will be able to spot any potential errors.

In the meantime, a few suggestions:

Typically, when using one of the single firewire port Saffires (Pro 14, Pro 24/DSP) in dual unit mode, you need to use the power supply provided with the unit.

Also, although the instructions do show 2 Pro 40s, there is a table on page 13 showing how the i/o of your Pro40/Pro24DSP setup relates to the DAW.

good to see Focusrite here on the forums answering questions - for a competitor.  Thanks Matt.

@

AT , both units are by them.. so yer why wouldn't they :)

even though it's not their official forum 

 Sounds like the OP is planning on using his VRM box to a much greater extent than I will be. I also find a support rep from Focusrite replying here to be both unprecedented and admirable. A support team actively looking for issues on other sites that are only present when there are issues to resolve speaks volumes about a company IMO. No spam or damage control defensive posturing, just support.
 My only Focusrite products are probably the 2 of the most haired brained ideas in DAW history. The DSP powered Liquid mix (convolution compressor and EQ) and now the VRM box. I certainly love the sound of their hair brained ideas and look forward to the next