TL:DR; This isn't a complete windows fix - but it does sound perfect though Chrome Flash and Adobe Flash/Air stuff - In the mean time I make do with a last.fm subscription and swearing at the developers of my computer.
I know this is an old post, and this may not be completely answering your question, but I've been battling with this myself recently.
Understandably the speaker fill is designed to poly-fill the problem but as an audiophile, I thought it sounded dreadful.
I never got the sound configurations to work correctly but after tracking down and installing the correct drivers and (You can now perform these tasks with Realtek HD Audio player) fiddling with the audio app, I stuck upon an interesting bug of which I hope someone can shed light upon.
full 5.1 surround sound works with HD films and anything built for high def audio. MP3 files played though any locally installed player are 2.1 channels, however audio playing though Flash is true, beautiful crisp 5.1 (joint stereo it seems) music.
For example; BBC iPlayer, Last.fm, youtube, quicktime etc... all crisp sound out of all 5 channels - iTunes, VLC, winamp, foobar and others are 2.1 channels.
This is most notable using Chrome and Firefox and tends to be dependant upon which application you use within Safari.
In essence - There is a small step I've missed to make this work with my current setup.
Within Realtek HD audio I have the following settings:
- Speaker configuration: 5.1 speaker configuration (If you only have 2 and 4 channel, you need updated drivers)
- Optional Speakers: Center, Subwoofer, Rear Pair
- FullRange Speakers: Front left and right
- Enable Bass Management
By setting other options within the interface will cause the software to add crap/phasing/cancellation sounds to the audio.
Things that fudge up the sound:
Setting Surround Speakers option. This will add an odd low phase fuzz and make the channels modulate it seems. You don't need this option
Setting Speaker Fill option. This just add a snow to the back speakers, cancelling some of the channels and trying to send the extrapolated frequencies to the rear, badly. Just don't do it
Setting Room environment. This is the nearest option on the net I've seem to a successful 5.1 setup but it also applies a reverb to the sound. Badly. Try it, then listen to your favourite song :s
Using the Main Volume Balance. Trying to set the balance with the software causing the same effect as the first surround speaker option. Best using windows default for this if you can. Apps usually have this internal, else use the windows one
Over using the Room Correction: Small changes in the distance and decibels of the speakers doesn't cause a massive problem. But if you pimp a speaker with large values (e.g. 10 dB's) phasing occurs. Try not to change the dB level on any speaker more than -/+5
So if anyone can add more to this - I'll hand you an upvote. I doubt anyone will read all this, but it's in the interworld now -