the age/bus type of the card will have no bearing. It will just be the output level from the card in general. Dont use the speaker out level, since this has already been amplified by the sound-cards on-board mini amp, meaning more introduced noise.
Most new sound cards dont have a spkr out/line out option anymore, I guess they assume most people use amplified speakers nowadays.
Maybe you could try another sound card? I use a Vibra 128, cheap card, works great..