I want to purchase a used line 6 quarter stack. I did not see any specs in my manual for the speaker outs on my spider 4 150. When you plug in, do your internal speakers mute? Can I run just one speaker out to an external cab or do I have to run both? Any help would be greatly appreciated. I can't find any info on what happens when you run the speaker outs. Has anyone else had any experience running external cabs? Any help would be greatly appreciated. THANKS.