How can I get two NVIDIA GPU's of different generations (Kepler + Pascal) to run in my PC?

Question

I've built a new PC with a GTX 1080 last summer, and I still have my old 690 lying around over here.

I know that it's not possible to use both cards in SLI, because they have different chipsets, that's NOT what I'm asking for.

I'm mainly using this PC for graphics design and Rendering in Octane. It'd give me a nice little boost of around 30% (judging by the official charts) using my old card as second renderer or for AI noise reduction. (Therefore, my idea isn't pointless, please don't try to tell me that if your arguments are just: "Oh, it won't perform any better in games!")

I also know that it IS theoretically possible to use multiple graphics cards of different generations for Octane as a lot of people have run tests on such configurations.

When I try to insert the 690 in my PCIe-Slot and connect adequate power, both GPU's fire up and Windows starts normally at first, but:

a) it uses the 690 as primary card to drive my displays (which is no option, since I'm using multiple displays requiring DisplayPort to work properly and the 690 has only one DP-connector)

b) I can only get the displays to work properly if I install a driver for the 690 instead of the 1080

c) the 1080 isn't detected in Octane anymore (it is still detected in the NVIDIA device manager, though)

d) the PC crashes with a bluescreen after a few minutes.

So does anyone know with what driver trickery I can get this to work? Or am I overseeing some compatibility issue? Or is this a problem of the OS (Win10)?

Any help would be appreciated.

Hardware:

CPU: i7 5930k

RAM: 32GB DDR4

Mainboard: MSI 7885-023R (based off X99A-Architecture)

GPU1: Palit GTX 1080 8GB

GPU2: GTX 690 4GB (Manufacturer is Zotac I think, but I'm not entirely sure)

Power supply: 1000W bequiet (so it is very unlikely that this is a power issue)

Answer 1

Install separate drivers in Windows Device Manager.

When you first run the Nvidia installer it will ask where you want to unpack it. Extract both Nvidia packages to separate directories, name the directories like nvid690 and nvid1080.

Then right click "This PC" and click "Manage".

Then click on "Device Manager" and expand "Display Adapters" so you can see both of them.

Right click each one and install the drivers from the nvid690 and nvid1080 directories.

To do this click on "Browse my Computer..." then "Let Me pick from a list..." then click on the "Have Disk..." button and browse to the nvid690 or nvid1080 directory and select the driver you want to use for each.