If you are not using more than 16 input channels, you can use channels 17-32 for complete separate monitor mixes. All you need to do is to select Analog 1 as input source for channel 17, Analog 2 for channel 18, 3 for 19 and so on. Now channels 17-32 are your "monitor mixer" with own processing. Of course you need to unroute input channels 17-32 from Main Mix L/R.
It makes sense to dedicate one or two effect slots to the monitor mix. A reverb in FX C and a delay in FX D, for example. Additionally you set the "monitor" FX sends to prefade, because you are not really "mixing" auxes. Fixed settings (prefade) are appropriate for monitor mixes.
The 16/16 "frame" would be ideal, but the concept also works with 20/12 or 24/8 channels. Not all channels need a separate processing, so use the spare channels you have for the few signals which need special processing.