I ahven't finished putting my computer together, so I haven't heard what the lower end one sounds like. Compared to the Audigy in my current computer, the I/O is a little less:
- no Firewire port (not so important as it is integrated in many MBs)
- no Midi game port (you need the front panel for this)
Also, there are no internal plugs to go to the front panel for cases
I have a 6.1 set-up for speakers. If I can plug a microphone in, but there's no jack left for headphones if I hook up my speakers. My speakers actually have a port to plug headphones into that sits in the volume/base control (on a wire that goes to my desk), but you can't plug in a mic through there.
The front panel that Creative provides for everything except the Xtreme Music does have a front panel (takes on 5 1/4" slot) with a bunch of connection options. They also provide a remote control that I guess would be useful if you were running the computer as more of a media center and were not sitting right in front of it.
I looked at onboard sound, Audigy 2 ZS and the new X-FI cards. Since I'm building a new computer, I decided to get the most recent card. I saw no need for the extra front panel or ram, so I went for the basic model. I'm not sure what use the OP intends for his sound card. I'm going to use mine for game play, watching movies and listening to music.
Michael