Its a phantom center channel... The 2 front satellites create the illusion of a center channel over the monitor. And as for the digital, i believe that they are dolby digital (as opposed to pro logic), but dont quote me on that.
As for the speakers, for $99, GET THEM! I have 2 friends with these and they are very good. Not as good as my klipsch's, but for $99 you cant beat that.
Comparing these 880's to my klipsch's i'll put a chart for each:
880's ($99 right now)
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+ Bass (that sucker can shake the crap outta a room, 8" woofer)
+ Remote Control (really helps)
+ Digital
+ Price (yeeep)
Klipsch ($279-$399, depending on 4.1 or 5.1)
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+ Bass (even more than the 880's, it has 2 woofers in the same enclosure, they are a little smaller, but pound alot more)
+ Highs (it has a horn tweeter, makes the highs sweeter and projects more)
+ Wattage (400 watts total, can really fill a room without distortion, and these suckers can get LOUD!)
If i think of any more i'll add them... Feel free to comment and add to this...
Personally, if you can afford it go for the Klipsch's, but thats a big price difference.. Its up to you...