Peavey 6505 - High \ normal gain input comparison

Hi guys, before buying this head (june 2011) i asked myself a lot how much differences there are between High gain input and normal gain. why 6505 has 2 guitar inputs and the 6505 plus (a little more expensive for his double eq.) has only 1 guitar input? i don&know but i needed someone who tells me why, so i tried to give you an idea how theese different inputs sound. i used 2 diffent guitars: an ibanez MTM1 (old version with emg&for lead channel and a jackson RR24 for clean parts (same emg 81 of mtm1). signal chain: mtm1rr24----peavey6505-----mesa boogie recto 4x12(v30)-----SM57-----alesis multimix 8-----garage band-----Imovie-----metalheads! m/ i don&used any kind of post processing, no compression etc...only a little reverb on clean tracks