I am curious as to what is actually incompatible with what, the firewire card and motherboard or the firewire card and the interface that is connected. I have a situation with two identical pc's with identical firewire cards but different interfaces.
The interfaces are a Focusrite Saffire pro 40 and a Saffire pro 24 and Mixcontrol 3.4. Mixcontrol 3.7 was tested also and made no difference. The firewire cards are Vantec cards with a VIA chipset. In my old PC (HP) I used a SIIG card with a TI chipset and it works perfectly with my Pro 24 but does not work with my interface in my new PC so I picked up the Vantec in hopes it will work and it works perfectly in the new PC.
However the pro 40 does not work with the Vantec card in either PC. I did not test it with the SIIG yet though. I was wondering if anyone knows for sure if it's the interface that needs to play well with the card and not necessarily the card and the motherboard?
Sonar Platinum is not a factor here as it does not have to be launched for Mixcontrol to fail. For a sort explination of what is wrong. Mixcontrol does not communicate with the interface. I will get more detailed if need be.
PC specs: ASUS H170M Plus System board Intel(R) Core(TM) i5-6500 CPU @3.20GHz 16GB Ram Windows 7 Pro

Did you try the 1394 Legacy driver? That is the usual fix.
Windows 7 should already have it. You have to select it.
Go to Device manager/IEEE 1394/Driver/Update Driver/Browse my Computer/Let me Pick.
Choose the 1394 Legacy Driver, reboot.
 
And for those people running windows 8, 8.1 or 10 the 1394 legacy driver is not included.
You have to download, install, then switch the driver per the above instructions.
Here is the download link. it works for Windows 8, 8.1 and 10:
https://support.microsoft.com/en-us/kb/2970191

I believe all the Saffire units should run on the VIA chipset, but Focusrite did say there was an issue with Win10. I didn't realize the legacy driver could be downloaded, so that is nice.
 
In addition to that driver, the only other thing that comes to mind is the firmware in the interface. Does the 40 run on one machine but not the other? If so, Mike's comment on the legacy driver may be the solution for you.

I remember that the via firewire chipsets are often the cause for 
difficulties, but my expieremce on that  is years ago.
Since I´m running a firewire card with TI chipset 
I forgot about problems soundcard wise.
regards
 

With Firewire, it's down to the specific Firewire chipset... *and* the specific audio interface.
Most times, when you see folks having issues with a Firewire audio interface, they're NOT using a TI chipset Firewire controller.  Using a quality TI chipset Firewire controller increases your odds of success (compatibility).
 
The SIIG TI chipset Firewire controller is a good one... and works well with most Firewire audio interfaces.
If you're having issues with an audio interface connected to that controller (especially an older Firewire audio interface), try using the "Legacy" driver (as was mentioned).
 
 
 

my via FW chip works fine w/ TC in Windows 7.  But many people have "fixed" an interface problem by using a TI chipset.

I had a Saffire Pro 40.  It would ONLY work with a T.I. chipset interface.  I tried it on others and it either would not connect or have intermittent connection.  The Saffire Pro 40 (and most audio equipment) use the "DICE" or "DICE II" chipsets and they only want to "see" (work with) T.I. Chipsets.
 
Here is what Focusrite says about the chipsets:
 
https://support.focusrite.com/hc/en-gb/articles/207546925
 
 
 

fireberd
I had a Saffire Pro 40.  It would ONLY work with a T.I. chipset interface.  I tried it on others and it either would not connect or have intermittent connection.  The Saffire Pro 40 (and most audio equipment) use the "DICE" or "DICE II" chipsets and they only want to "see" (work with) T.I. Chipsets.
 
Here is what Focusrite says about the chipsets:
 
https://support.focusrite.com/hc/en-gb/articles/207546925
 
 
 

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.

Why are you not using Mixcontrol 3.7 for both Focusrite's download seem to recommend them for both.
 
I am running a Pro 40 with 3.7 on a TI chipset under windows 10

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.