No worries at all, Wee... you're quite welcome. There really isn't any sort of crazy voodoo to PA systems, just a lot more of stuff you already know about. Good to know that you've got the cross and graph taken care of, you're one step closer! The A&H mixwizard is a great console, which one are you getting?
Unfortunately, I don't have any direct experience with the GX series so I can't really speak to their build or sound quality, so take whatever I say about them with as much salt as needed.
Overall, they look like it is a cost-conscious, market research / needs driven design where some compromises were made to fit a specific application. Not a bad thing, but the lack of a bridge mono mode and the lower power ratings lead me to think that they may be usable, but not a perfect match, for your application. Bottom line is that power is power, and they will drive speakers... but they do seem to be geared more towards the band that already has a mixer and a pair of high packs and will never need anything but a 2 speaker stereo setup.
In all honesty, the GX7 looks like it would be a pretty good match for your tops, and it may even scale out just enough if you wanted to chain out a second 8 ohm cabinet on each side or swap your 8 ohm 1x15s with a pair of 4 ohm 2x15s. You'd be nearing slightly underpowered, but it would probably be survivable.
It is really the lack of bridge mono that is throwing me... out of the box your subs will be underpowered by 400 watts with a single GX7, and getting a pair of them and running them "single channel driven" (still not exactly sure what that means aside from being less power than a mono bridge) would leave you wanting for 200 watts per sub. It makes me think that for the money / number of amps, you may be able to get a better bang for your buck and a better match elsewhere.
Again, the bottom line is that they will power the speakers and being based off of the PLs may even sound better than the RMX amps, which are clean workhorses, but not hifi by any stretch.
Style of music can also factor in as well (we play melodic thrash metal). I run a QSC RMX2450 on a pair of Turbosound TXD-151s reenforcing vocals only, and it can have a hard time keeping up with 2 half stacks attached to guitarists who believe "turn down" means "turn up more, but just do it less", my SVT4 + PR410HLF, and a thunderous drummer. Other styles are far less abusive of power ratings.
Again, headroom is king... you can always turn a loud amp down and the overdriven amp sound is great for instruments, but it just makes a PA system sound cheap.
Another consideration... does your crossover have a stereo low out, or is it mono only?
- a Peavey Maxsys system, it's quite old in today's market but still packs a mighty punch and i'm more than happy with the sound quality. The thing is i'm about to purchase a new Allan and Heath mixwizard desk and will need some nice new amps to complete the set up. The spec for the PA is:
