The input channels on the Coliseum PA are essentially the same, but I would jumper one of 1 or 2 with one of 3 or 4. I wouldn't jumper any more than two, because you'll just be loading down your guitar signal and losing high end - but if you like a dull muddy sound, go for it because you are not going to hurt anything.
You will have to use a split cord to jumper as each channel only has one input jack.
I believe Leslie West used one of these heads for guitar - it should have more low midrange... but I don't know if he combined channels.
