if you want to make decent recordings of rock guitar,
then get a decent mic, a decent amp, put it in a good sounding room, and do it right.
it's just not going to sound the same as doing it with a guitar port.
a guitar amp sounds NOTHING like a monitor playing back guitar sounds.
the mic will hear the difference,
and it should be obvious.
that's not to say you can't experiment with all kinds of tones using that methodology,
but that's not really what you are asking about.