akschu,
You don't necessarily need more servos (although that would be best), but higher torque servos would help a lot. If you do use more servos you don't have to put them each on a different channel. You can use a Y-harness to hook up two servos on one channel, or if more servos you can use 3 y-harnesses to control 4 servos, etc.... I put an OS 91 FX in mine and put Hobbico high torque servos with metal gears and they did just fine for me, I had plenty of servo.

Hope this helps

Ken