Oh, ah, well. That's just bass ackwards. You shoot for the sound you want, not what sounds, "better." So stick your mike on the guitar amp and tweak it until the both of you feel that's what you're going for. If it's nothing you like then use the line input. Record your settings and see if you still like it the next day.

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You don't need a weatherman to know which way the wind blows - Robert A. Zimmerman