What are the impedance and sensivity ratings of these speakers?
JBL's are usually easy to drive. With that said, are your mains towers of bookshelves. With towers, regardless of impedance and sensitivity numbers, I usually like to drive them with an external amp.
For your setup, I would recommend a mid range Yamaha, Harman Kardon, or Denon receiver to drive the center and the rears. Purchase a 2 channel external amp to drive your two mains. Parasound is a very good brand that wont cost you an arm and a leg.
If you are not too finicky about sound quality, you can even purchase a multi-channel external amp that can drive all your speakers.