DirectX Issues (Steam)

I'm running an Early 2015 MacBook Air with Intel HD Graphics 6000 and an Intel i5 processor with 8GB of RAM with Windows 10 64-bit through a Boot Camped external drive. Overwatch, RollerCoaster Tycoon 2, and Portal 2 all run perfectly fine - heck, Portal runs better than it did in Mac mode.

However, games with the pop up that says "Installing DirectX" as they boot in Steam don't work - they start to boot and then stop immediately. Sonic Generations in particular says three .dll files (XINPUT1_3.dll, d3dx10_43.dll, and d3dx9_43.dll) are missing and then doesn't boot.

I've found that I need DirectX 9, I believe (Windows 10 has DX12 installed automatically). The DirectX installer within each game's files (and the same file grabbed from numerous sources online) fails the installation, saying to check the .log for the issue (which I can't make heads or tails of). The Direct End-User Runtime Installer on Microsoft's website, which I've been directed to as a be-all fix repeatedly, does not work and fails to install as well with an error with advpack.dll. I've updated my graphics card drivers, updated Windows 10 twice, reinstalled multiple games repeatedly, and even turned off antivirus and nothing works. This is getting increasingly frustrating as I can't play the majority of my games, which is what I did this Boot Camp process for in the first place. Boot Camp shouldn't be the problem; as I said, some games work just fine and I haven't found anyone else through hours of Google searching that had the same problem as me.

Can anyone please help? I'm desperate at this point.

Just to check you are using this download which does work with Win10?
"http://www.microsoft.com/en-us/download/details.aspx?id=8109"
Should be obvious, however some I have come across dont realise that you need to run DXSETUP.exe from the folder it downloads to, should run with Admin privileges however try Running as admin if it's failing.

Link keeps coming up on here as access denied so copy between the quotes.

I've downloaded that and ran the same file out of Steam game directories multiple times, both as admin and not. Each time it fails and says I need to check the .log files for what went wrong.

Yeah, the DXSETUPexe doesn't work. It's the same installer within Steam games. I put the .dlls Sonic Generations was asking for in the folder and it doesn't ask for them anymore, but it does give a new error code. After inserting the .dlls, most of my Steam games are still not booting. No error code, they just don't run.

Humour me, run sfc /scannow, it has happened in the past that a missing or corrupt system file could cause problems installing directX.

One of the first things I tried actually, haha. No errors were found.

So, uh...hypothetically speaking...would running this whole ordeal in Windows To Go be an issue...?