You are correct. Most, if not all high end sound cards neglect this feature. In fact, there are very few soundcards that allow this. BUT, you can run both the onboard sound (with the header for the front panel AND a soundcard at the same time. There is a simple program for this, I just cannot remember what it is called. I will see if I can find it.......
Intel E6300/Nouctua NH-9U w/dual 92mm Panaflos
XFX 680i LT
Patriot PC2-6400 2X2GB LL
2 X BFG 8800GTX in SLI
Enermax Revolution 620W PSU
ASUS 24X DVD/Seagate 250GB SATA 2/THermaltake A90/Windows 7 Ultimate 64