Yes, bass guitar. :)
Use a vintage model plug in if you have one, like a Neve or Urei. It will work wonders for the woofiness. You will also need to apply a parametric EQ to the bass.
HINT: Generally speaking, you do not want to have identical frequencies running on all instruments. Typically, you want the kick drum and bass guitar to go the deepest. I would high pass the guitar tracks at 80Hz and see how it sounds. If they are still muddy, try edging up the high pass 10Hz at a time until you are happy, but don't go over 150Hz.
If you ADD 60Hz on the kick drum, for example, make sure you CUT the same amount on the bass guitar, and then fine tune to taste.
Subsequently, you can drop a lot of the mids and upper mids from the bass guitar to make more room for the electric guitars.
Mixing is a very complex thing to explain in text, and there really is no right or wrong way to do it.
Hope this helps!!