Spider Iv 75 in Spider IV / Spider Online Posted February 19, 2014 Any who.. My experience with this amp is a very positive one. Way to go Line 6! PS: The HD500x doesn't sound too shabby through it. Connected via MP3 input from the 500x's output. I was surprised. Sent from my iPad. Thats interesting...I guess the MP3 input is sort of like an fx return. Wouldn't have occurred to me to try that.