It is not a PnP card so you have to run the hardware detection procedure or install it manually if not detected.

It's the same outcome, I've tried hardware detection, but no success. I've followed the same installation order/procedure as on the previous build (which is working as mentioned earlier) & nothing happens. I don't even get a unknown hardware notification or something like that.

That's strange indeed ... I would try thefollowing steps: Reserve the IRQ (5 and 7) to legacy ISA in the BIOS settings. Let the BIOS controll the resources and select PNP OS > NO. Disable Printer Port in BIOS.
Try another ISA -Slot (if available). Another idea was to lower the cpu speed to check if it is a speed issue and check the supply voltages but as the card works fine in DOS thats obviously not be the problem.
I hope you can get it to work!

Go to BIOS and set PnP OS to No, then in Device Manager go into device profiles and set Port IRQ and DMA exactly as jumpered by the card.

I am surprised that your SB Pro is even working in DOS with such a fast system. In my experience those cards will start to have issues on a fast Pentium. Maybe there's something I don't know and there are ways to make them work on faster PCs, but I would look into that as a possibility.

It's actually working in Win98 now. All I had to do is to manually add SB Pro (in add hardware) & install procedure went fine, without any errors, unlike before when I tried auto detection and it would hang in the middle so I'd have to reboot.
Thank you all, glad it's working now.