Recording Acoustic guitar - using line signal?

Hi, I want to record my acoustic steel string guitar while I sing through a condenser mike. I do not own two condenser (I do have sm57 and 58 though), but recording the guitar via its built in preamp would save me so much time in many cases. Any advice on how to get the best result using line signal? Could I use some X1 plug and some magic trick (or even plugin) to make it better? Oh - and I know I should "get a Neumann and a perfect room", but I can't right now. Cheap fixes greatly appreciated. Thanks!

I personally can not STAND the sound of an acoustic recorded line in. Unless you have one of those built in mics, those can sound ok. But the typical line in on an acoustic I personally find is never usable. I hate it. With a passion. Just what I think! I'm not saying don't use it, I'm just saying that I almost certainly wouldn't.. 

You may find you can get away with using the one condenser mic for your vox, and try to angle it down towards the acoustic a little. Experiment to get a good balance. How loud you sing and play guitar becomes extremely important here as you're basically mixing live and cannot really adjust much after. I have done this before to record quick takes and it can sound ok.

That's the simplest option, but you'll probably get better results by blending in a second recording. Adding a 57 on top of this for your acoustic could work well too. It can fill out the lows and you'll get a bit of extra highs from the condenser. If it suits your voice, the 57 may work great on the vox with the condenser on the guitar. You may still get away with blending a little extra line-in from the acoustic too.

Make sure you position your mics to reduce phase issues. You can do a little manual shifting in SONAR afterwards to line things up, but because you have two different sound sources so close together, there is only so much that will help. The best result will be with appropriate mic positions. One option for this may be to set the condenser and the 58 up in an XY configuration, with one mic pointing at your mouth, and the other at the guitar. Equidistant spacing between mics and mouth, and mics and guitar.

But your best option for sound quality is to record the two takes independently. You'll eliminate phase issues and have most mixing flexibility. In this case I'd probably use the condenser for both. Double micing the acoustic might sound great too. It all comes down to experimenting and seeing what works for your voice, your guitar, and the sound you want. There is no right answer to this - only options to try and see what fits.