Frankie:
The Guitar and the Bass player needs to furnish their own amps and speaker system, I've never found anything that will carry my guitar sounds without breaking down, or just not getting the true sounds I like.(I've been playing for over 60 years)
I tried my Strat into my Z5500 and it just will not carry it! even in a small room. same thru my 8 channel Yammie PA.(wh 4-15" yamaha clubs). My rig for the guitar is a 1964 Fender Duo Showman Head that I added two 8" speakers right into the Head. One 8" is a 100 watt sub base speaker the other is a 100 watt 8". This sets on top of speaker cab. with two heavy duty 15's and a 120 watt bass horn. (also have second cab Identical for ext. to oposite side of the stage). This rig probably weigh's 150 or more pounds. And will walk around the stage if playing outside to a good size audience. but delivers crisp highs and crowd moving bottom end on a normal gig. Have never found anything that will replace it.
I guess what I'm trying to say is that a guitar or a bass has to have extra gear to handle its powerful drive, and the run of the mill amps and Pa's just won't take the abbuse. and produce the quality in the sound.
The Dawn system sounds like it might be good for a keyboard, but looking at the ad, I don't think I would buy it over the Z5500.
It's hard to get the right system for each different user, and usually means some trial and error and wasting some money in the process, and end up toting a bunch of gear. I always hauled the PA system and my gear, and made each player responsible for their own.
For the keyboard the Z5500 can't be beat for the money and the sound is excellent and better than really needed for live to the audience who is banging Knife's and fork's and talking etc etc.
My choice would be.
Use the Pa for vocals for the band/or in a pinch (backup amp).
Each player provides his/her own system.
Logitech Z5500 for your keys/vocals Use Gary's setup......
.........Pose