Gary, you shouldn't have any problem with the power that the Z-5500 system has.
I just played a dance in a 3000 sq. foot hall with the Z-2200 (satellites on stands as you described). This was a very "live" hall, long and narrow. In fact the hall is so live that I had to face the satellites backwords, pointing directly into the stage curtain. No amount of equalization seemed to work. In spite of the sound directed into the curtain, there was plenty of volume with power to spare.
Since I don't sing, I can't attest to how the z-2200 would sound with vocals under the weird setup that I had to use.
We'll be waiting for your report from New Year's Eve.
Best of Luck,
Walt