|Both aren't great.|
If the SoundMax is based on the recent HD Audio standard, use it and save a PCI slot. If it's an older AC97 chipset, use the SBLive!.
HTPC | Pentium M @ 2.82GHz, 2MB L2) | 4GB | 1.0TB | Radeon HD5750
Blu-Ray | Win 7 Pro | HDMI out to Onkyo TX-SR707 AV receiver