Input 1 and 2 are the same other than that fact that Input 1 (?) is also connected to the loop out.
The loop out would allow you to integrate it into a system without using the preamp out, thus double amping.
Say you have a CD Player that outputs a Line Level signal (no volume control) which you then run into a preamp for a speaker system, but you want to use that CD player for your headphone amp as well (LG). You could connect the CD player to your LG then the Loop Out of the LG to your Preamp and get the same Line Level signal for both.