Have you tried emailing Focusrite directly? They have always responded quickly for me and would be the best resource (plus they seem to keep track of what doesn't work with what). There are six variables at play - MOBO, FW card, interface, FW driver, interface firmware, and MixControl version.
 
That article Jack linked is a good read, and I saw two things I didn't realize in it - "TI XIO2200A - tends to work with most systems, however there are known compatibility problems when used with Z170 and X99 motherboards." and "Please note that you need to be on the Standard Windows Driver to use the OHCI Tool.  If you are on Windows 7 using the Legacy Driver please revert to Standard Driver..."
 
After seeing that second one I think I am actually on the standard driver vs. the legacy one. Their link is broken, and my VIA driver is from 2006 (6.1.7601.17514) - when I googled the legacy driver it seems to actually read "(Legacy)" at the end of the driver name, which mine does not have.
 
Edit: I just ran their OHCI tool and got these results:
OS: Microsoft Windows 7 64-bit Service Pack 1 [6.1.7601]
  CPU(s):
    Processor:  Intel(R) Core(TM) i7-2600K CPU @ 3.40GHz
    Physical:  1
    Cores:     4
    Logical:   8
    L1 Cache:  32 KB   (8)
    L2 Cache:  256 KB  (4)
    L3 Cache: 8192 KB  (1)
  Installed RAM: 8159 MB

  Microsoft 1394ohci.sys [6.1.7601.17514]
  Microsoft ohci1394.sys [6.1.7600.16385]
  Microsoft 1394bus.sys  [6.1.7600.16385]

Looking for OHCI 1394 Host Controllers...

1:
  Vendor : (1106) VIA Technologies
  Chipset: (3044) VT6307/VT6308
  Revision: C0
  Status :  Active
  Details:
    Subsysten VendorId: 1043
    Subsystem DeviceId: 81fe
    Max # isoch Rx contexts: 4
    Max # isoch Tx contexts: 8
  Max 1394 Speed Capability: S400
  Support:  Compatible, no known issues.

Done.

I found a link to the OHCItool.exe that Focusrite references in the article I linked.
 
Click Me 
 
Focusrite in the article states:

If you are unsure about the compatibility of your firewire chipset, please download and run OHCItool.exe. If it reads "This controller is not compatible with DICE drivers" or "Compatibility Unknown", then you'll need to replace your firewire card with a compatible one.
 

Jim Roseberry

Mosvalve
This is not true because the pro 40 was and still does work great on my HP PC with a VIA chipset. My Pro 24 is currently working with a VIA chipset on my new PC but my SIIG card with TI chipset doesn't work in my new PC.

It depends on the exact Via chipset... and the specific audio interface.
Not every Via chipset Firewire controller will work with your audio interface.

I don't think VIA has every updated their chipset past 2001.

kitekrazy1
I don't think VIA has every updated their chipset past 2001.

I doubt that VIA hasn't refreshed their product line in over 15 years.  I'm using an SIIG card with a via chipset and it works fine with my Motu. 
 

I knew I had read something from RME about this. Prepare for more detail than you need but here you go. One of the main issues is the voltage in the chipset.

http://www.rme-audio.de/e...echinfo/fw800alert.htm

SF_Green
I knew I had read something from RME about this. Prepare for more detail than you need but here you go. One of the main issues is the voltage in the chipset.
http://www.rme-audio.de/e...echinfo/fw800alert.htm

They are talking about 1394B which is firewire 800.
It doesn't really help this thread since we are concerned with 1394A, which is firewire 400.
Thanks for posting the link, though. It does offer some insight into the RME. They don't have any incompatibility problems with any of the firewire 400 boards.

You say you haven't tried the SIIG card... I think that's the next logical step.
 
I've been through four FW devices, with two different PCs (including a Saffire 24), and have never had FW compatibility issues.  FWIW, both PCs were built by me - using components known to be "DAW friendly" - and the FW card was always a SIIG (PCI and PCIe) with TI chipset.  This was on Win 7 and 8.1.
 
Are you using a PCI FW card?  Be aware that some of the newer system PCI slots are "bridged", which have been known to cause problems for some users.  You should be using PCIe if possible and, of course, TI chipsets.  As Jim suggested, if all else fails, try the legacy FW driver.

I want to thank everyone for all the great info. It turns out that the Pro 40 will only work with the Vantec VIA PCIe card using the legacy driver. Go figure. My Pro 24 works fine with the Vantec VIA PCIe card using either driver. You gotta love computers.
 
Thanks so much for all your help.
 

I know this thread is marked solved.
 
However, a note on the OHCItool.exe.  I tried running it in Win 10, native and in compatibility mode and it never finds any 1394 controllers.  However, I booted up Win 7 and ran it and it found the 1394 controllers without problems. 
I don't know about Win 8/8.1 but I suspect it won't run on that either.

fireberd
I know this thread is marked solved.
 
However, a note on the OHCItool.exe.  I tried running it in Win 10, native and in compatibility mode and it never finds any 1394 controllers.  However, I booted up Win 7 and ran it and it found the 1394 controllers without problems. 
I don't know about Win 8/8.1 but I suspect it won't run on that either.

Older thread, I know, but Firewire hasn't died yet. It is, however, riddled with problems (99% caused by Microsoft). This is an informative read: https://support.focusrite...gb/articles/207546925. Furthrmore, at the bottom of the article, a revised ohciTool.exe is available. I'm on Win10, and it worked.

Also, it should be noted that in other article online, Focusrite stated that the legacy 1394 driver (which is no longer included in Microsoft Win 10 and subsequent builds) is NOT required for modern Saffire interfaces. Read it here: https://en.audiofanzine.c...ws-10-problem,p.2.html