AUX are for connecting other internal sound sources to the card, perhaps another CD drive or MPEG decoder.
MBPRO is for connecting Creative Modem Blaster from what I know.

Tiido wrote on 2020-04-21, 15:15:

AUX are for connecting other internal sound sources to the card, perhaps another CD drive or MPEG decoder.
MBPRO is for connecting Creative Modem Blaster from what I know.

Ok, as you can see in the picture the aux headers are not populated, can they still be used?

You need to solder few extra components to make them work in addition to the connectors themselves, you can see that the traces go to non populated components. I don't know what the values of those components might be.

Tiido wrote on 2020-04-21, 15:19:

You need to solder few extra components to make them work in addition to the connectors themselves, you can see that the traces go to non populated components. I don't know what the values of those components might be.

I guess that the components are the same as the CD in part, i want to connect another sound card to the aux input for proper OPL3 sound.
I dont know if the aux input will be shown in the mixer software.

Why not just use the second "CD In" for that? I mean, it's already there and you don't have to modify the card. Only downside is that the volume control is shared with CD Audio.

The CD connectors are parallel, and that will short whatever you connect directly with CD drive outputs, which may not be ok for one of the devices involved.
Populating R82 and R90 with 10k resistors should make AUX2 functional. Value of these resistors will determine the mix level.
AUX1 should be mixed with CD input, R21 and R22 should be populated with probably 10k range resistors to make the input functional, R32 and R33 may have to be also. I have the card but I don't have it accessible right now to take any closer looks.

You are not going to short anything, unless you wire GND the wrong way. If you have two CD-ROM drives, you can also use both connectors. You just need to make sure that the wiring is 100% correct.

If anything, you'll add some resistance to the input(s), which will make both sources a bit quieter. But that's where the mixer comes in handy to compensate.

Maybe on open loop feedbackless output will not mind being directly connected to another output, but that's not how most audio signal outputs are made. There's always gonna be a closed loop feedback setup and if it is connected directly to another output they will begin to fight each other and correct for the unexpected output through the feedback loop. If a 1k+ resistor is added then things begin to work out.
It is like connecting two linear power regulator outputs together, their outputs will not be perfectly same and they begin to fight each other, one trying to maintain its idea of what the output should be and so will the other. End result is excessive current draw that can result in damage.

Tiido wrote on 2020-04-21, 16:17:

The CD connectors are parallel, and that will short whatever you connect directly with CD drive outputs, which may not be ok for one of the devices involved.
Populating R82 and R90 with 10k resistors should make AUX2 functional. Value of these resistors will determine the mix level.
AUX1 should be mixed with CD input, R21 and R22 should be populated with probably 10k range resistors to make the input functional, R32 and R33 may have to be also. I have the card but I don't have it accessible right now to take any closer looks.

Thank you for the advice, i will do the modification and report back the results.