we work with what you give us, pics, vids, etc. all can aid us to respond in a more detailed or on point "fix" or idea of what to do next. Take pics of the side of the amp where the gain is and make sure it is clear and post it up.
nvm, i see what you mean about the two gain settings.
http://www.sonicelectronix.com/item_23986_Soundstream-RUB1.2500D.html
Its for various input voltage, if your preout is 2v, switch it to 2-8v and have it all the way up, or have it on the .5v-2v and have it all the way down(i think thats how it works). lower the input voltage means more gain.
But as far as when you get your XL, before hooking it up, check the triple joint, suspension, etc. to make sure its 100% and then hook it up and see if anything seems out of place.