External sound card

Hey!

I'm thinking of buying the Logitech Z-5500 5.1 system for my PC and well, I have a couple of questions for you:

1. Which is better do you think, built in sound card or the DAC in the Z-5500? (Analog or optical)
2. How much difference do you think one would notice from the built in card compared to an external sound card?
3. Have anyone here tried a Creative Sound Blaster X-Fi Surround 5.1 (That's their external X-FI)? In that case, is it any good?.
3.1 Did you experience an audio delay, some people claim there can be up to a second in audio delay.
3.2 Some people claim that the drivers use a huge amount of system resources, is this true?
4. Does anyone have any experience with DTS and DD from a chip like mine using analog or optical (S/PDIF)?

Specs:
Sound Chip: ADI AD2000B
Motherboard: Asus P6T Deluxe V2
OS: Windows 7 x64

ADI is one of the better onboard sound, but it is still onboard sound the sound quality is good, but not as good as if you had a dedicated card. I have the Z 5500 and I used them with the optical and I have used them using analog connection via my Creative X-Fi Titanium and I like the quality of the sound from the x-fi better then letting the Logitech do the processing. External sound cards are crap they grab the digital signal via a noisy USB port and are just not good no matter what manufacturer makes it.

The x1 X-Fi Titanium Fatality is what I have I love it has great sound quality, you should also look at the ASUS D2X they are great cards too.

It seems like the only difference is the shield, some LEDS and 64 instead of 16 MB of ram.

I just ordered a set of Z-5500 and an Creative X-Fi Titanium

Thanks!

Maybe you're not using Mplayer Classic (or the home cinema variant) but how do I get the most out of movies with it? Do I need to add some external creative filter that handles the DTS decoding or will the built-in one suffice?