A few things.
First, try getting a tube screamer (or better yet, the Maxon reissue--the OD820 is what I have, as they supposedly sound a lot better than the current Ibanez versions). Use just a hair of gain from the tube screamer, with the volume knob at noon and the tone knob to taste (usually between 9 o'clock and noon for me). You'd be surprised at how well it tightens that low end up. Again, I'm not really using the pedal to get extra gain (just a tiny bit, 9 o'clock or lower), just to tighten the low end up.
Secondly, once you get the guitars in the mix, make sure you filter out all the very low end (anywhere from 60-100 Hz and below). The bass has to fit somewhere...make sure you let the bass and kick provide the real low end of the mix. Too much low end in the guitars will give you nothing but trouble in the mix, take it from me. Most of what makes a good or bad guitar tone lies in the midrange areas...make sure the lows aren't cloudy or flubby and the highs aren't too sizzly, then dial in the mids to taste.
Finally, if you still struggle with it, look into a multiband compressor like the Waves C4. Multiband compressors only compress certain frequency ranges. I definitely do not compress guitars when recording (except maybe acoustics or cleans). If you look at an electric guitar file, it's almost a square wave already, so there's no point (IMO). However, if I need to control the low end, I may compress just the low mids with a multiband, say from 65-250/300 Hz or so. Just be careful, because compression (multiband particularly) takes a long time to master (I'm still getting the hang of it), so it's easy to overdo it or do it wrong.
In fact, to me that low-mid area is one of the toughest areas to get right in a mix. If you don't control it, you end up with a flubby and unfocused mix. If you carve out too much of it, the mix sounds too thin.
Anyway, I hope this helps and let me know if you have any more questions.
