It was plug and play for about three days (Add Y splitter for power and display port cable from 5080 to Monitor). Not sure why but today the system is really unstable.
Workaround Update 3: Perfect timing for BL4 launch as I found a "fix" for the bad PCIe lanes in Win10. Just click the button on the AGA cable and agree to the pop-up to disable the AGA and unplug. Then plug back in. The link negotiation inside of Windows will yield no errors. A shutdown/hibernate can come up with bad links but the WA persists across suspend/reboot.
Later update 2: Forcing the 5080 as highperfadapter seems to be fine for basic tasks, benchmarks and casual games but will eventually freeze when extreme gaming loads placed. Only waiting for a "good boot" works at extreme gaming load =/ (like 1 in 40 boots it seems)
Update 1: Turns out the AGA/Win10/5080 can come up in less than perfect PCIe/BIOS handshake. I must of been fortunate with my initial boots but appears the issue is confusion that Win10 has dealing with the PCIe errors and then handing off the Gfx workloads back-n-forth with the onboard discrete and the AGA. This terrible passing of programs around trying to optimize just craters the performance/stability. Using @ssj92 post about dealing with different cards in his M18x system was a good workaround. I noticed an improvement when I had assigned a program to use the 5080 explicitly and had wondered if there was a global setting like no 2080 for GPU workloads.
Even on "bad boots" the 3d mark is 2 or 3 fps less than perfect rather than completely freezing (later testing has exposed this to not be 100% workaround). All the display related programs only run on the 5080 with the "DirectXUserGlobalSettings" (only laptop display shown attached on 2080) I cannot disable the 2080 or the internal LCD remains on after the 5080 takes over on Windows boot and I don't want to burn the image into the screen. I've currently disabled the iGPU in device manager to try and further limit the "Gfx program shuffling",
2080 just sits idle and turns the LCD off while I use external monitor via Display Port from the 5080.
FYI I recommend HWInfo64 default boot on startup with the 5080 sensors displayed. Thus I know immediately if I have best gaming fps ready to go or need to try again.
Old debug progress and rant posts:
Just really strange since last night I was getting sudden drops in the IJ full circle to 5 fps then back to 50+ which did not happen Saturday (the day I added more RAM). Now the game refuses to launch properly and runs at 5 fps the entire time and me messing with the settings with a choppy mouse hasn't helped.
I read that the best way to unlock the full potential of the AGA is to manually disable the internal/laptop gfx discrete (somehow in BIOS such that they do not show in OS) such that the system only looks to the AGA card. I haven't discovered those steps but perhaps I am getting unlucky BIOS enumeration which is giving the 5080 trouble w the OS? Sometimes if I have the other cards disabled in the device manager then strange things happen. One being the internal LCD does not cleanly hand-off during boot and stuck with logo when the 5080 monitor takes over. (not always though)
I've seen some really great scores from Reddit with the amplifier. I went to check the how-to and post was removed by a filter. Does anyone know the steps? Guessing I hook up the display to the back of my card in the alienware amplifier.
