Dolby Digital on ac3 passthrough issue

[1GKar]

I can play DVDs, using PowerDVD 4.0's (OEM version) SPDIF, and get Dolby Digital on my AV receiver without concern.
When I attempt to play DivX movies I can only receive two channel 48000hz audio.
The movie's audio formats are verified as 5-channel 48mhz in both GSpot and Nandub.
If I attempt to configure AC3filter to SPDIF I get nothing. This may not be unusual as I do not use digital through my soundcard. I use a USB device (Xitel's Pro HiFi Link) to passthrough the AC3 format.
Any ideas on how to get 5-channels working?

I would rather not be forced to pay for a PowerDVD upgrade to allow 5 channels. It would cost me upwards of $50 my currency.
I am at a loss to understand how the SPDIF works with PowerDVD on DVDs, but does not work with HDD DivXed movies, though readily admit my knowledge of codecs and their inner workings is very limited.

[setarip]

Have you tried playing the DivX files under Windows Media Player v.6.4 instead of Power DVD?

[1GKar]

Setarip,
I have now. Same deal; no AC3 though not sure how to set up audio specs in this version?.

Thanks for the response

[1GKar]

I think I have an answer for my issue, though it is not one I like given my hardware.
I pulled this from avsforum.com:

You mentioned that if you upgrade your system to a 5.1 setup you'll have to get a soundcard with digital out.... Keep in mind that most receivers also have 5.1 analog inputs and analog in combination with a multichannel soundcard is certainly a viable option also. If you decode the audio on the HTPC than in addition to DD/DTS you can also have multichannel WM9 and multichannel game audio if that matters, whereas if you connect just via digital than you are restricted to 2 channels unless you are passing through DD/DTS from a DVD (except for some NForce type motherboards which can encode multichannel audio into DD and send to your receiver over a S/PDIF ). Just thought I'd mention the option.