Hi.
I think you have to get propper gain on the inputs of you channels.
If you have set the recording point other than post-preamp, the processing (HPF, gate, PEQ FX insert, comp, AMM) will also change your levels.
According to the specs, 0 dB meter = -18 dBFS
This means, if you set your level to 0 on the scale of the CQ, the reccording will be maxed at -18 dB.
The headroom is defined to be 18 dB, the CQ and your reccording will clip if you go beond +18 dB on the scale.