You say you are competing with heavy guitars, bass and drums?
Maybe dump those JBL's for a pair of these as the manufacturer describes this model as a solution for exactly that competition

They are probably in the area of $750 each, but a man has got to do what a man has got to do.
Grab a pair and make those cockroaches inside the walls, dance

Click the pic for more details.

Use a mixer....I use a small mixer[Alesis multimix 6fx] for my small set ups..It sits on my keyboard, and gives me control right in front of me...I can blend the laptop[MP3's], my keyboard and a couple of mics[with effects]...You never know when you have to adjust volume and EQ thru the job..This is one thing that is not worth the short cut...One AC plug and two more cords!!!

MrEd, those look cool but the JBLs are on like 5 out of 10 and theyre blowing me away playing with the band so I think I'm good at this point.

Fran, I have a small mixer like yours, the Yamaha MG10 or something, and yea I started using it instead of running mono, and I like the difference...plus it gives me some extra parameter controls. I just need to mount it on a stand and ill be good to go.