Reply: "Full" sound usually means "adequate bass" or "adequate low frequencies." So if your system does not sound full, the bass or low frequencies are being lost somewhere in the signal path. First look on the bottom of each PCC-160, where you'll find a bass-tilt switch. Make sure it is set to Flat, not Cut. The Cut position reduces the bass and makes a thin sound.
Next, see if your sound system includes an automatic feedback suppressor. Maybe it is automatically turning down low frequencies in an attempt to reduce feedback. Try to bypass the unit and see if the sound gets fuller. Some automatic feedback suppressors have a wide notch filter rather than a narrow notch filter. A narrow notch filter is required to reduce feedback, but a wide notch filter also affects the tone quality of the signal -- not desirable.
See if your sound system includes a graphic equalizer. Normally it is connected between the mixer output and the power-amplifier input. Maybe some of the low frequencies are turned down too much on the graphic EQ in an attempt to reduce feedback. Again, try to bypass the unit, or set it to flat (center the sliders) and see if the sound gets fuller.
Check your mixer EQ (equalization) knobs on the mic channels and make sure they are set flat. If the low frequencies are turned down, this will make the sound thin.
Do the headworn mics sound thin, as well as the floor mics? Maybe your loudspeakers are weak in the bass. Do they sound OK when you play a CD over the sound system?
Typical PCC-160 placement is three mics about 1 or 2 feet in from the stage edge, about 10-15 feet apart. The PCC-160 picks up in a broad vertical angle, so it's best to leave it flat on the floor. Also, putting it on a stand changes its frequency response (tonal balance) because of the phase interference of delayed sound reflections off the floor. So for best tonal balance (best fidelity), just leave it flat on the floor. This will also improve the bass. The PCC-160 is a boundary mic, which needs to be mounted on a large surface to have adequate bass or fullness.
Maybe a mic cable is wired in opposite polarity from the others. This would make two PCCs "out of phase" with each other, partially cancelling the bass if both mics are on at the same time. Make sure that all mic cables are wired pin 2 hot on both ends. If one mic turned on sounds full, but two mics turned on sound thin, cable wiring is the problem.
If possible, turn up one mic at a time (follow the action) to reduce feedback.