Hi Milsancho,
First of all, please relax.
You've decided to go against all advices and use an HD 4000 generation card for modern Windows (post-XP) so expect troubles.
Monitor detection was a plague for these gpus so back then I decided to patch the drivers in order to FORCE monitor detection in all analog outputs. This is why you'll see a "generic no PnP monitor" even if the output is disconnected. This allows you to go into Windows display manager and extend the desktop whether or not there's a physical monitor connected.
Then you will face a random situation as Windows tries to restore the last known working configuration and may send your desktop to the unwanted monitor until things finally settle. If you just accidentally boot the pc with a different monitor layout (e.g. having unplugged one of the screens) things will turn random again.
Having suffered this myself, I wrote the "algorithm" that you can find in Eiusdemmodi's guide, that works for the most typical configuration (single monitor).
Believe it or not, all this trouble caused by forced detection was less bad than having to physically add resistors to trigger detection.
To make things more interesting, you want to use 15 and 31 kHz monitors at the same time. You can do it, but on this older hardware you can't install different custom modes per output, so all of them will be mixed and available for both outputs.
In your situation, I'd be using a newer card like the ones you posted above. Then use the VGA for 15 kHz with EDID emulation, and a suitable HDMI->VGA adapter for 31 kHz, since you don't need low dotclocks for this (HDMI by design has a lowest dotclock of 25 MHz).
PD: I've used cards with ribbon cable for VGA all the time, no issues here.