I guess that I can help you on this...
Well, you need a 5.1 sound card(any SBlive5.1s or Philips accustic edge..etc) and a 5.1 multimedia speaker system.. such as midiland S4-8200 or even S4-7100 or DTT 3500.
Also you would need a DVD Software, like WinDVD 2.3 DTS. If you can find G9 to 6 RCA connectors and 3.5mm to 2 RCA connectors in your area, this setup can give you 5.1 for DVD, 5 channel for gaming, without ever having to unplug things...
The idea here is you don't really need the ADS2000 decoder in 8200 to get AC-5... If you just connect your soundcard to the 8200 speaker via G9 to 6 RCA and 3.5mm to 2 RCA connectors, and use WinDVD 2.3DTS to run DVDs, you will get AC-3. when you play games, the 5.1soundcard will output 5 channels to 8200.
If, however, you have S4-7100 instead, the setup is just like the above and the connectors are much easier to find in the states.
If you wanna go for Promedia 4.1, you can still achieve 5.1 effect by buying another 2.1 for the center channel. But adding the cost of SBLive 5.1(you can get the value version now, which is about US60, if not go for 5.1MP3 or 5.1Gamer which would cost about US90) the cost of WINDVD 2.3DTS or later, which is about US50 and Promedia 4.1 US300 plus Promedia 2.1 US180, the total would be around US600.
But if you go with 7100 for the speakers, your cost would be just around US300.
Or if you go with 8200 for the speakers, your cost would be about US400.
So it's your call...