If the lack of IGP drivers is true (and Win8 version doesn't work), can you make do with a video card? I seem to recall that in the absence of a specific driver that Win10 will attach a "VGA" version which should allow you to use the card if you have adjusted BIOS. Start with monitor attached to IGP port, you boot into and then reset BIOS to the PCIe slot. Then you shut down and install video card and attach monitor to that. Then you can set up drivers for the card and proceed with the upgrade.....[ ]....
Some of this is not the best idea. Most BIOS settings for IGP, to standalone video card are automatic.
You plug into IGP, then the system reads it and sets the BIOS to IGP
You plug into a separate card, the system reads that.
IMHO, you should never set the BIOS to one over the other. Again, IMHO, there is no need. But more importantly, should the system be locked into the PCI-E mode,if the card fails, you'll need another card to light the monitor, or you'll get squat when you try to boot up..
I've made this mistake once by locking a BIOS into PCI-E only, and thank god I had an old 8400 card laying around, or I swear I'd have had to throw the board away.
In a somewhat related incident, I tried to put extra RAM into an i3-3225 system, in which I had installed a GTX 750 ti. So, I was half drunk and made every mistake I thought could be made by, trying to plug the RAM modules in backwards, sweating all over some ICs on the mobo and whatnot.
When I finally did get the RAM installed, I booted the system and it wouldn't fully boot into Windows. As it turned for whatever reason, the 750 crapped out during the process, even though I didn't tamper with it directly. I incorrectly assumed mu faux pas with the sweat and the backwards RAM ruined the board. As a last resort, I yanked out the 750, thinking I could save it for my next build. With an "oh well, what the hell have I got to lose", I plugged the monitor into the board's IGP port, and lo and behold, the system booted up perfectly.
A word to the wise, never change the BIOS video setting to anything other than "auto".