With that card do you have the Mini-jack to RCA cables?
You could get the AudioSource Amp 100 for
$70 plus shipping. Each amp is a 50 watts/channel at 8 ohms and 61 wpc at 4 ohms (so it is 4 ohm stable).
Later on when funds become available you could get a beefier amp and simply regulate the AudioSource to surround duty.