Although I have only a single graphics card in my PC, I have seen numerous threads from folks who have multiple monitors. I don't recall that they had to modify their DSDTs.
A search may be helpful.
What is it about the AVID software that requires you use a DSDT? If you are really licensed for that software can you get vendor help on using it without using a DSDT.
One of the ways a vendor may lock their sw to a specific mac is the info in the smbios.
Maybe you only need to modify the smbios.plist so that AVID sw recognizes your PC as a particular MAC. There are loads of threads about working with smbios including using a specific serial number. I had to change my serial to get cloud access. {also there are indirect ways of modifying smbios using choices in Multibeast}.
On another item in the thread: Even though you got a little bit father along the install/operation using the wrong rev DSDT, you might find it better to use the correct Rev 10 DSDT for your motherboard.
Finally
You might search the net for info about problems with the AVID software licensing. Frequently eave legal sw has such problems. Although the AVID forum[if any] might be the best place for that info, the info could be anywhere on the net.
It seems to me, you have several ways of attacking your problem, The dsdt is only one way.