XBMC can play through analog sound cards no problem. You just need to set it up correctly.
What I believe I said was that XBMC can't play through the "default" device, you need to tell it exactly which device to play through in XBMC audio settings, and so changing the default device will have no effect on where XBMC audio goes, but this applies only to Frodo, not Eden. Eden allows you to use the default device.
You certainly don't need to buy any new hardware to fix this.
