Kind of a specific mixing board question.

There is a very good likelihood that you will experience a latency delay if you live monitor the mix through the computer.

This is why a lot of mixers and or interfaces with mixers on them, have "zero latency" monitoring where the signal is split from the pre to the headphone jack, and to the input to the computer.

I do not know the specifics of your setup, but you would have the mic go into the mixer, and the mixer send to both the computer and the headphones. The Computer will then process and output to the stereo input on the mixer and be output to the monitors (which will be off during recording).

Inside sonar, you can then trigger "input monitoring" to hear the processed signal "live, but there will be delay, and the delay will get worse the more effects you throw at it (they all need to be processed in serial).