Ah! That explains it. So I connected Mons 3 & 4 to the Asus mobo's onboard DVI-I & VGA, checked that its latest driver was installed, and the monitors work just fine. So I'll remove the 8800 now.
Cheers, pendragon1. Have a pleasant day.
Hi.
System details ..
Mobo: ASUS Z87-PRO.
CPU: Intel Core i7-4770K CPU @ 3.5GHz - x64-based.
RAM: 2x 16GB Kingston HyperX paired - 31.9GB usable.
Power: 1200W.
Disks: No disk changes, with system disk 3.63TB free.
Op Sys: Windows 10 Pro v21H1 Build 19043.1889 64-bit.
Monitor details ...