5.0 speakers with X-fi Xtreme Audio

Make sure you are in 'Entertainment mode' (Audio Creation Mode doesn't have the feature needed available), and go to the Creative Console Launcher.

Here, press the Speakers & Headphones button, and then press the THX logo on the right when the new layout pops up.

Go to the Bass Management tab, and here, simply set the Front Left/Right to be 'Large', instead of 'Small'.
This will guide more bass to the main front speakers, without an additional subwoofer.

Least, it should work that way
I hope this helps

EDIT:

Its a shame you aren't using the additional Flex-Jack digital module, as it does allow bitstreams of Dolby/DTS out.
Plus, has a setting for 'Bitmatched playback'. This makes the sound card ignore all Windows Bass/Treble enchancements, etc, and allows your amp more control in this area.
I have it set on my Logitech Z-5500's and it sounds much better with this setting on, and set to 96KHZ out.

It should be the same for all X-Fi cards, as they are built on the same chip, and should all be THX certifed I think, at least.

Have you installed all the programs that came with the drivers? i.e, the Creative Audio Console, Creative Console Launcher, etc?

Without these, you won't be able to access the specific options you need.

Go to the Creative website, and download the programs:

http://support.creative.com/Produc [...] reme+Audio

Choose the right Windows and there you go

"PCIe Sound Blaster X-Fi Xtreme Audio Pack 1.03.0002
Filesize : 63.76 MB Download
Show Details"

That contains the Creative Audio Launcher etc that you need, but you may as well update your drivers too to the latest. They just wipe over the old ones without any issues.

I hope this works for you.

Flexi-Jack:

Your card is better than I thought, and is actually one up from mine.

You don't need the flexi-Jack as yours has Optical In/out built into the card. Mine doesn't, and only offers a 3.5mm female adapter to plug in a special extra component to add Digital/co-axial etc.

So the features I listed if your digital inputs to your amp supported 96KHZ, and all that jazz, would allow you to do the Bitstream out once you install those programs.
You'll have to give it a test

But yeah, there are settings to allow the amp to handle DTS/Dolby Digital encoding anyway, or there should also be an option for the sound card to, but if your amp supports it, you may as well use the bitstream out function instead.

I hope this works for you. Good luck

Oh... the same card links to the bigger version...

Try downloading the software for that card then to see if it enables all the features.

However, since it may be the cut down version, it may not offer everything the full versions offer, but still functions using the same X-FI chip, so should have the same power.