I'm in a mess with sound - help!

Guys,
Can anyone help here?
The only problem I have with Win7 is sound.
I use a Audigy via digital 5.1 output to my Creative 5700 receiver via optical cable. In Vista (and XP before) everything is great.
In Win7, I get output, but after a while I get distorted buzzing and playing some games, the sound cuts out completely.
I've tried some of the suggested fixes, e.g. changing to high sample rates, using Daniel K's drivers, etc. to no avail.
So, I decided to try the onboard Realtek sound. I installed the 2.14 drivers, and although the sound seems quite stable, there are 2 problems:
1) the quality is poor. there is no depth to it. Is there a equaliser (or something else) that can boost bass and treble?
2) I can only get 2 channel stereo. No option for selecting 5.1 or anything that I can see.
Can anyone help with any of this? If I bought a newer card (X-Fi Extreme?) would that solve the problem?
Thanks.

Yes, the problem is my setup doesn't have any of these options as I don't have speakers attached to the on board audio. I use the optical out into my receiver.
Any ideas?

Thanks. Yes I do have these options, but they don't really help. I have no way of selecting 5.1 speakers in menus.
For years, working with my Audigy was simple:
1) connect via digital din to my 5700 Inspire
2) select 5.1 on the 5700
2) go to 'manage audio devices' in Control Panel, select 5.1 and test.
Then when I'm, playing games I get full surround sound, i.e. if I move 360 degrees, then if someone is talking to me in the game the voice goes full front to back etc.
I can't achieve this with the Realtek sound.