Okay, if you can't find the SidSpeed entry in your Registry, using Regedit, then you need to create it.
First thing: You need to look for the correct ID number for your Firewire controller in the Registry.
To know what's the correct ID go to:
Control Panel->System->Hardware->Device Manager
Find IEEE 1394 Bus Host Controllers - click on the "+" sign next to it to show the sub-entry:
"Texas Instruments OHCI Compliant IEEE 1394 HOst Controller"
Right click on that, and select "Properties"
In the "Details" tab you can see the Device Instance Id.
This is the ID number that you should look for in the registry. Write it down now, or keep the Properties window open for now.
For example only, my ID is:
followed by a "\"
and then 4&6B16D5B&0&18F0
Yours may be different. In any event, you'll want to use YOURS.
Click your Start button, click on "Run" and in the window that opens, type "regedit" (without the quotation marks).
Go to: HKEY_LOCAL_MACHINE and click on the "+" sign to open its contents.
Go to: SYSTEM - open its contents
Go to: CurrentControlSet - open its contents
Go to: Enum - open it
Go to: PCI - open
Go to: the ID number you found above, starting with "VEN....." and going to the first "\" - open it
Go to: the number that followed the first "\" in the ID number you found above, like "4&6B..."
In other words, go to
In the right side of the regedit window, you should see the contents of this last entry.
At the very least, there should be something called "(Default)" and a second entry called "SidSpeed".
Now, here's the crucial bit: If there is no entry for SidSpeed, you can create it by right clicking anywhere in that right side of the Regedit window, and using the pop-up menu that appears, create a new item. Name it SidSpeed - just like that, all one word with the two capital "S"s.
Once it's created, you need to enter its value. Do this by right clicking on it, and select "Modify" from the pop-up menu. A window will appear with a field for "Value data", and two radio buttons for selecting either "Hexadecimal" or "Decimal". Select "Hexadecimal", and enter a "2" in the Value data field. Click "OK" to close the widow.
Restart your computer.
If the SidSpeed setting was indeed the source of your problems, then your Fireface should start to function properly now. If not, well, sorry about all that...
Now that you've created the SidSpeed entry, you can find it again easily by using the "Find" function in Regedit, found under the "Edit" menu item.
If you like, you can experiment with entering a "3" instead of a "2" in the Value data field mentioned above, as the value of SidSpeed. This is supposed to enable speeds faster than Firewire 400 (which is to say, Firewire 800), but there is some debate as to whether this is actually necessary. I've found both to work with my Fireface 800.
Fireface 800, Firmware 2.77
Drivers: Win10, 3.125; Mac, 3.36