I ordered a pair of JBL PRX618s-xlf subs last week, & they'll be here tomorrow. I understand how my board works, and I'v been giging & running sound for us for a year or so now, so I'm not a complete newb. Here's my thoughts. We are a five piece, two guitars, bass, drums, vocals, and we always run in mono. I'm thinking of taking the sum mono out of the board, into the 1st sub, link to the 2nd sub. Now engage the x-over on the 2nd sub, up to my powered RCF are 312, and lastly come back to the last top. This would be one continuous chain, and seems like it will work, I don't know that it's ideal though. I did have a question about the JBL subs, they have a L & R input, and the specs say 2 x 500w for the amps. I'm wondering if I only use the L or R input, & I only getting 1/2 the power? Should I be splitting the signal going into the subs? or will the sub use both amps when it only see's one signal?