Need Help for a dual screen setup

Hello Everyone,
a great pleasure to take part of this amazing and outstanding community. First of all, I'm a newbie and with a friend of mine we decided to build up a hackintosh. Thanks to tonymacx86 we focused our efforts on an old setup we had in order to run mac.
Despite few little graphic issues (like glitches when using Photoshop) our main interest was a dual screen setup (1440p + 1080p screens resolution). Unfortunately, only VGA really works and so we were not able to setup the latter setting. When using HDMI the screen was not recognized by the system. So, reading on the forum we flash the bios of our card (using Palit etc etc) and we didn't solve this dire issue. We are also willing to buy another graphic card but we would be sure to nailed our goal (namely this setup). Please look at our specs:
Graphic Card: Asus GeForce GTX 750 Ti 0 MB
CPU: 3,5 GHz Intel Core i5
Motherboard: Gigabyte GA-H97-HD3
We are running OS X El Capitan 10.11.4
any suggestions?
thanks in advance

I'm surprised you got VGA connection working with the GTX 750 Ti card as Apple hasn't supported VGA in decade.

From where did you download your copy of El Capitan?

Well, first of all thanks for your quick reply.
I downloaded el capitan directly from the Apple Store from my iMac.

Would be really glad also I you'd be so kind to direct us to some helpful links such as the installation Guides: GTX 750 Ti.

Please notice the exact model is the following:
https://www.amazon.it/gp/product/B00ICUGOP0/?tag=tonymacx86com-21