just drill a hole or use a spacer who used to hold a vga card for instance and solder a mini-molex to a male 1/8 phono jack. Molex pins are easy to edit but better have it right first, the pinout on the card is usually silk marked on the card or is very easy to guess from the pcboard, you could use that site https://th99.bl4ckb0x.de/ if you want to double-check.
Some sound card have jumper style connector (like your picture) or mini-molex, 3 or 4 pins. Check it out before. You could do like I once did and solder directly to the cd-rom connector... just make sure your computer current is cut first, like I once did not 😁
The picture you show is just a female 1/8 phono jack screwed to a spacer, you can say it's cleaner, but you will have two male jack on the back of your computer, it's your choice. No more digital cd-rom but it will free-up your line-in. I know the SB32 have a CD slider in it's mixer, not sure about the gus classic but I think yes, better check it out first.