Windows 7: 5.1 in ut2k4

Hi, I have a Gigabyte P55-UD3P mobo, and it has has the following for it's on-board audio

Realtek ALC888 codec
High Definition Audio
2/4/5.1/7.1-channel

Unreal torni uses the following for it's ingame Audio

3D Audio
H/W 3D Audio
H/W 3D + EAX



is there any way I can get 5.1 surround, or do I need a sound card cos atm the best I can do is get the back speakers to out put the front 1's, which is not good enough...
(note that I do get 5.1 surround outside of the game. in WMP and other progs...)

Thanx for any help on this...