I am ironing out the last of the little quirks on my new system build and trying to get the onboard Realtek audio on my Asus P5W DH Deluxe to drive my old Creative speakers.
I am running Windows Vista and when I go into Configure Speakers... I am unable to get them to all work correctly. If I set the Audio Channels to 5.1, I am able to get FL, FR, FC and Sub but no channel from the RL, RR or RC. If I set them up as 7.1, I get sound out of all of the speakers but I have to uncheck the side pair.
I would prefer to either drive them as 6.1 or 5.1 and select the upmix switch on the speakers themselves to create the RC channel. My concern is that directional sound may not be processed correctly due to the 7.1 with no side speaker setup. The motherboard detects the conenction and I only have an orange (FC/Sub), green (FL/FR) and black (RL/RC/RR) connectiors, all of them corresponding to the ports on the motherboard audio.
I also still have my old Creative Audigy 2 ZS but I am trying to keep this system as simple as possible and using the onboard audio seems to be a good choice since it's 8-channel and several years newer.
Well, I finally broke down and installed my Audigy 2 ZS just to see what I was missing. Night and day, the Realtek must have been driving the speakers completely incorrectly, I can't really nail down what it was but the sound quality is amazing. I am now getting directional sound in World of Warcraft and my MP3's sound 10 times better. I guess I will just keep an eye on these Creative beta drivers to make sure they don't cause an instability with the rest of the system.
Did you ever resolve this - I have a similar problem using an ASUS Barebones system with Realtek Audio.
In my case, connection same as yours, Green/Orange/Black back panel to speakers. I set the speakers to 6.1 in the HD audio manager and the 3D test works fine (no rear midspeaker of course but all others driven apparently correctly). Plain sound from Winamp or any other player gets stereo on front right and left and subwoofer. No centre front or any rears.
No options to drive it differently from Windows though (XP Pro). The control panel shows the hardware as stereo but I can't select anything else.