I'm recording vocals and one, possibly two acoustic guitar tracks. I have a m audio firewire 410, cascade m20, sm58, and an sm86 and am using cool edit pro. I'm obviously recording the vocals through the m20, which sounds decent with enough gain, but the problem I have is what to record the guitar tracks with. Should I use the 58 and take off the grille, is the difference between a 58 without a grille, so big of a difference from an sm57 that I should go and buy one? If all else fails how would the m20 hold up to recording an acoustic guitar?