i would suspect that the motherboard mic input is only analogue. avoid it at all costs.
since i no longer have to produce for tv i've found usb audio input to be quite acceptable, especially when used with a good mic.
i have a simple xlr to usb cable, a 48v phantom power supply, and can use any of my xlr mics with excellent results (senn me80, samson omni, sure sm 58). in fact i actually bought a cheap $35 bm800 condenser mic on ebay that sounds really quite remarkable (though it really does need phantom power to bring it to life).