Question How should I set the analog input level to get optimum performance
The maximum analog input level you can have is + 22 dBu. You have to turn the input level on the front down to -6dB to be able to handle such hot levels. The meter read out is in dBFS. This is a digital meter so 0dB is really the maximum level you can have here, otherwise you will experience digital overloads. It is best to keep some headroom and have your input level reading between -18dB and - 6dB. This way you can apply the compression, use the spectral enhancer, and the makeup gain, without risking overloads.