Here's a few ways:
Mono or Stereo Out(s) of mixer into Drive Rack PA.
Low Out(s) of DRPA into XS-1200 then connect Subs (one to each channel of XS-1200). If DRPA only has one low out, use Y cable to get to both inputs of XS-1200. This would give you the 4ohm load for each channel and the amp would supply 1100 watts to each sub. You can't bridge mono that amp and connect the 2 subs (daisy chained one off the other) cuz you'll be goin down to 2 ohm load...not good for that amp.
OR you could go out of the DRPA and set each xti2000 to bridge mono and connect one sub to each amp. That would give you 2000 watts to each but you'll be over the peak power rating of the MRX-518's (1600 watts). If you don't clip your output signals you'll probably be alright. Remember the .80 to 1.25 rule. Basically when matching amps to spkrs you want an amp that gets anywhere within that range of what the spkrs PROGRAM power rating is at the specified ohm load.
Now if you opted for the first suggestion you could now use the xti2000's for your mains and monitor(s). Come out of your DRPA's mid/high output (s)(the boxes aren't biampable) and connect to one of the xti2000 set to bridged mono mode. Connect to input 1 on xti and then connect both mains (daisy chained) to spkr/out on xti chnl 1. Now you're running a 4ohm load with an amp that will push 1000wts to each box (ttl of 2000wts). This is within range for those boxes.
Take an aux or monitor send from your board and connect that to one channel of your other xti2000 for the one MRx-512 monitor. This will be a little under powered for your application but for now it should work. Buy another one of those then you will set the xti to bridged mono mode and connect the same way as above.
Now for the other stuff. If the DRPA has limiting, compression, crossover, etc all built in then that will allow you to use your outboard other dbx stuff for channel inserts (lead vox, kick, snare etc) and the DRPA can be set to act as a limiter before it hits any of your amps inputs (protects you if some idiot comes up and cranks the main fader outs on your board while you're not looking). I would not use the BBE unit on your mix at all. Maybe as an insert for a guitar/acoustic etc...but not on your overall mix. As for the xti's internal processing..I would try it both ways. Find the spkrs in the menu and select them, run the system and see what your ears tell you. I have heard many people go that route and others simply bypass that stuff, adjust their crossover freq's in their DRPA, set their EQ's in their DRPA and their fine with it. It's going to take some trial and error.
As for the mounting of stuff in the racks, I would go with whatever you would need for "must have" shows in one rack and then a smaller rack for the add on stuff that might be required for a larger show. I know I have one rack that houses 2 amps, 1 x-over and 1 mono 31 band EQ (for FOH/Mains). This rack goes with us to all shows. It's our "Must Have" rack. I can run mains and monitors off of one amp (XS-1200) and still have an XS-900 as back-up in case of failure). I can also put the XS-900 in bridged mono mode and run it with my subs for slightly larger rooms. My other rack contains dbx stereo comp/limiter, 1 Peavey 31 Band Monitor EQ with FLS (feedback location), and some select rack fx that I can patch into individual channels if needed. We use an Allen & Heath MixWizard so it has fx already in it which are fine for what we need and I don't need the Peavey EQ for monitors most of the time hence that's why rack 2 only goes out for larger shows where I'm gonna be running multiple monitor mixes. Lastly I have one small rack that houses an additional 2 amps (CE-2000 and QSC-1450) that I use in conjunction with the other 2 racks above. All of this allows me the capability to run a system as large as:
2 Bag End 18" Subs (with Eminence Omega Pro-18A's in each...modified the ports). XS-1200 can be bridged putting 3000 watts to these OR the XS-900 can be bridged for 2500 watts to the subs.
2 JBL MPro 225 Mid/High boxes for mains/FOH (only take them out if it's a larger room). If these are used, they are run off of the XS-900 (one box per channel for a total of 1800 watts or 900 each) in conjunction with the XS-1200 powering subs...gives me a total of 4800 watts FOH. Not bad.
2 Yamaha Club SM-15IV's (used mostly for mains/tops). One side of the XS-1200...each box gets 550watts. These are our primary tops that go out to most shows.
3 Yamaha Club SM-12IV's. Other side of the XS-1200.
1 JBL Sound Factor 112 ....our singer loves it. Either on same side as the XS-1200 above or one side of the XS-900, or I can just use one of the other amps.
I believe that the way I have this system racked allows me to easily grab just what I need for the gig and not kill my back while trying to move one huge rack, ya know??
I'm not familiar with the input panel connections so I won't go there on that. As for the power conditioners....well I think you know what should be connected...all of the stuff Hope this helps.
Hey thanks alot for the advice Glenn. This is almost exactly the way I am running it now. xs1200 in stereo to the subs/xti2000 in stereo to mains/xti2000 in a+b to the monitor.
Glenn I just picked up a Yamaha cs15v floor monitor should I run this xti in stereo now or better to go mono 4ohm to each?
Also I think I'll try your recommendation and try the mains in mono at 4ohms ea. with the xti2000.
So I guess I really dont need the BBE 882i, maybe I'll sell it. Any suggestions what I should incorporate to make the best noticeable difference in my setup....effects perhaps? If so, any suggestions there....Lexicon?
Thanks soo much for your help.