how close are you setting the mic to the guitar and in what position /area.  Expiriment with mic placement first..  the closer the mic to you fingers the more percussive a sensitive mic is..  I have a condenser mic and I usually get my best tones from my classical guitar from about 3feet away facing slightly upwards (face of mic would shoot me dead in the chest. straight out from the 12th fret...  I also use some hard surface reflection areas to give the guitar more "room" sound.  This works well for me but may sound like crap for others (different playing styles, rooms, guitar, strings, mics, ect.).  I had to play around with mic placement doing quite a few recording takes before I found what I like.. I still work on it and who know I may find some mic'n technique I like better in the near future.   i have some 12string stuff I still have to record so I am gonna play around with mics and rooms and placement, till I get what I want.

mics I have and use... avlix , and Audio tech.. at4040, at4047.  used  akg c414(just purchased and love this mic so far).

You need to put the mic through a mocrophone preamp or line mixer to boost the mic signal, bring up the levels until you can hear the hiss and fine tune down from there
I use an AKG 1000s condensor mic and a shure sm-57. The shure is placed about a foot from the guitar and pointing just after the hole on the fret board, the condensor is about 18 inches away and positioned half way down the fret board. The mics the panned hard left and right.

The shure pics up the raw sound, the condensor the subtle acoustics, blend together and there you have it.

I learnt this technique from a book, it works for me.

Hope that helps

Denis