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powering two 4 ohm subs and two 8 ohm mains - need advice


I have two yamaha s115V mains (500W program handling, 1,000W peak at 8ohms) and 2 jbl mrx 518s subs (Power capacity (continuous/program/peak): 500W/1000W/2000W at 4 ohms).
I have a presonus studiolive 16.4.2 mixer and a few power amps. Two of my power amps are Behringer EPX 4000 (2 X 1200 into 4 ohms) that have a built-in CROSSOVER switch lets you put the amp into biamp mode, which sends low-frequency content (< 100 Hz) to the CH2 Output and the high-frequency component to CH1.
I would like to be able to use this crossover system to power stage right (8 ohm 500 watt main and 4 ohm 1000 watt sub) with one amp and stage left (8 ohm 500 watt main and 4 ohm 1000 watt sub) with the other amp. I have heard conflicting opinions from friends as to whether this will damage the amps and or speakers.
I plan to use this at small to medium size bars with crowds from 50 to 200 at the most. I may play an occasional pool party or private house gig.
I considered using an outboard crossover so that I could use one amp for the subs and one amp for the mains, so that I would not have the 4ohm/8ohm issue, but a friend of mine who has the same soundboard warned me that unless I bought a very expensive cross over, I would be degrading my sound due to putting an additional (lower quality) preamp after the high quality preamps that are in the presonus board.
Other amps that I have are a mackie FR2500 (750W @ 4 ohms, 575W @ 8 ohms) that I am powering 4 monitors with and a QSC GX7 (8&ohm; / both channels driven /725W, 4&ohm; / both channels driven /1,000W )
I bought the QSC GX7 because I was told by a salesman that I could use the built in crossover to run both of my subs off of this amp, but should have done more homework because it is set up the same as my Behringers. I can only send lows to side B and highs to Side A and cannot, as far as I know, use the crossover to send low frequencies to both sides. I will probably return this amp before my 30 days are up.
Thanks in advance for any advice.
February 29, 2012 @05:29am

It will not hurt your amps or speakers to run them as you suggest. I didn't study your post enough to discern if there may be a better option, but fear not. You can at least try it and see how it works out for you.
February 29, 2012 @04:35pm

Put very simply, stereo amplifiers are just 2 mono amplifiers in the same box. Each side is oblivious of the other's load and doesn't care about being loaded differently.
March 1, 2012 @08:52pm

Careful with the 518's. About 600 wpc is what they need. A GX5 would work nicely on them.
August 5, 2012 @10:11pm