soundblaster vs. on-board sound

this is strange. I have 2 systems, win xp and pclinuxos, identical soundblaster cards. received my mepis 6.5 live-cd.
With live-cd on the box with win xp, I had to switch the speaker pin to on-board sound to hear anything.
with my other box, using m6.5, the soundblaster card was picked up automagically, great sound.
any ideas?