For most sources(head units) you want the switch set to 1.0V to 8.0 V. The other setting would be for very low voltage sources, such as a portable MP3 player coming from the headphone jack.
Thanks Trumpet. That is what I was told by several people. Thing is, when it put the amp on 1-8 I get absolutely no bass. I can tell the subs are moving just not any volume. Even with gain at max. When I put it on .01-1 I get great bass. Any ideas?