If you've just been recording the guitar amp with a mic, you're missing out on half of the tone. Putting a DI in the signal chain gives you a clean guitar track to shape and mold. This will round out your guitar tone by using amp simulated software.
Use a DI that has a thru feature and plug the guitar into the DI and then run the thru output to the amp. This will give you a clean channel of the guitar performance that you can blend with the amp tone. Pro Tools now comes with the SansAmp plugin that will allow you to adjust the tone to mesh perfectly with your amp recording. Give it a go and see what you come up with. It can't hurt and if you don't like it, then you can just mute it.