I know, I know to a normal person it doesn't make any sense. Here we go. I need 8 channels, but they have to be matched L/R channels. Which means any amp with an odd number of channels will have one channel left lonely. So a 7 channel amp means I only have to add one two channel amp to it to get the requiste number of matched L/R channels. A 5 channel amp means I need 2 2-channel amps, a 4 channel amp or I would need to find an AT2003. So a 2007 means I can use the two channel I have lying around, while a 5 channel means I have to buy this amp plus another one.