Presonus Firebox and JBL LSR2300's help ???

[fatmatt]

Hey guys, long time lurker, first time poster here.

For the last year or so I've been using a Firebox with two 5'' LSR monitors via the 2 1/4'' Main Outs on the back. I recently came into a little extra cash, and want to expand my system. I'm an aspiring DJ/Producer and in the past I've used my monitors conservatively to play small parties. I want more output and more bass for both mixing and the occasional party. My plan was to buy the rest of the LSR line: 2 8'' monitors and a 10'' sub. But, I'm really really confused about how to make this work since there are only two main outs on the Firebox. I have a few half-formed guesses about using the SPDIF I/O RCA breakout on the Firebox and mixing through the sub, and I've tried (and failed) a couple different setups with RCA cables and the Presonus mixing software but I'm pretty much clueless.

In case it helps, heres the back of the sub:
http://www.proaudiostar.com/media/ca...sr2310sp_2.jpg

the monitors:
http://www.soundonsound.com/sos/nov0...LSR2300_02.jpg

and the firebox:
http://www.m-station.biz/id/componen...ca4da5ba7c.jpg

So- my question is, can I make this work without having to buy another interface?
Also, is there anything else I should consider other than buying two more LSR monitors?

Please and thank you !

[manchild]

Looks like you can bring TRS cables from the main out to the sub input and run a XLR to each monitor off of the sub.