I use Reaper to monitor and record acoustic and electric guitars. It reproduces the sound exactly without much effort. It's all about quality recording and playback equipment and the quality of the input signal.

If you want to learn how to use Reaper, here's a link to their video page:

http://www.cockos.com/reaper/videos.php

I've used just a few links on that page because all I need to do is press record, listen to playback, never really need to fuss with the sound because the input is reproduced exactly with default settings.