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As far as the Tascam goes, you don’t need the mono switch on unless you are directly monitoring your mono input signal (Input/Computer knob set to “Input”) and want to hear it out of both L/R channels.
You will generally want to leave the Input/Computer knob set all the way to “Computer”. This is necessary to hear anything coming from your computer through the Tascam.
With the Tascam ASIO driver selected you have to monitor through the Tascam (headphones or powered speakers or amp to speakers from the L/R RCA line outputs).
If you are using the right input for your SM-57 make sure you have the switch set to “Mic/Line”.
I would highly suggest doing some studying of the fine product manuals and then go back through the topics of this forum. It shouldn’t take too long to find approximately 9,574,863 other posts almost identical to this one 
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