Connecting Multiple Speakers/Subs
Im using a Numark Mixdeck, two powered subs (1 EV, 1 JBL), two powered tops, two unpowered Peavey SP15, and a QSC amp.
Whe I run my tops thru my subs, the side with the EV sub is great, but the side with the JBL sub I can barely hear anything, especially out of the Top. I will post a pic in a sec. I must have something connected wrong, or the EV is whipping the JBL ass.
Please help
How are you connecting this all up?? If we knew how you connected it up we would have a better chance at diagnosing your problem.
Does the JBL sub have a crossover, and is it set correctly?
you need a crossover to send the mixer output to the diff amps set at diff frequencies. u need to go mixer output-> crossover → then have the frequency set for ur tops and sub and passives. do NOT have your active speakers plugged into the amp, and an active speaker can be seen as having a built in amp
I would assume the powered sub would have a crossover. Then it would be out put from sub to amp to passive speakers, or out put from sub to active (powered) speakers.
But, we really can’t help with out more details. 
If this is your regular PA system, you might want to look into a balanced distribution amp if your mixer only has one pair (left and right) of balanced outputs. Maybe there are crossovers / processors that perform the same task and more.
you need to isolate the problem in the signal chain. Switch around the connections to see what works, what doesnt, and eventually identify the issue(s).