superfury wrote:

What was the on-board speaker on the Sound Blaster 1.X/2.0 used for?

You mean there's a speaker on these cards? I don't know of any.
The only thing I know is that you can connect your PC speaker to the Sound Blaster headers, which allows you to hear the SB through it. Afaik the line-out is still enabled, there's no switching.
I only had an SB Pro v2 myself, in which case I could connect the PC speaker signal from the motherboard to the card's mixer, and then connect the PC speaker to the SB Pro headers, so I could mix PC speaker and SB sound, and both would sound from the internal PC speaker in my case.
And also through the line-out (the party-capture of 8088 MPH was done via the SB Pro v2's line-out).

Whoops. I have mistaked the volume knob for a speaker, after looking at the images again:p Almost forgot those cards have one:p Do modern sound cards still have one? (Had mobo intergrated sound since, like 10+ years, which don't have one(never seen an onboard mobo volume knob) afaik)