Tony,
Having used both the Logitech Z-2200 and Z-5500 systems, I can honestly say the 5500's provide superior sound, greater depth, more coverage and for what you are using them for at the restaurant, the 5500 would be awesome. Keep in mind that with the 5500 system, you have a full 500 watts of RMS power, and when you consider the total number of speakers, including those on the keyboard itself, you have 8 speakers filling the entire room with sound. I have only used the 5500 for two Christmas parties, both of which had about 80 to 100 people in the room, and everyone raved about how great they sounded.
The Z-5300 does a great job as well, but does not have the same power and lacks a few other features found on the Z-5500 system.
Gary
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PSR-S950, TC Helicon Harmony-M, Digitech VR, Samson Q7, Sennheiser E855, Custom Console, and lots of other silly stuff!
K+E=W (Knowledge Plus Experience = Wisdom.)