we only have the 2014 models now but there is not really much difference from the 2013 models except they improved the app mode and maybe a little quicker btooth features..
1600-($249) am/fm/cd/rear usb/rear aux/ (2v pre-outs)front, rear, and sub out..
2600bt($289)- am/fm/rear usb/ rear aux/ (2v pre-outs) front, rear, sub out, b.tooth audio and phone
3600bhs(we do not stock this year)- (2v pre-outs) does the same as the 2600 but you get HD radio and you can add nav and you can also add sat
4600bt(we do not stock this year-(4v pre-outs) does the same as the 2600 but it has a 7 inch screen you can add nav with the extra piece but you can not add sat to this radio
5600bhs-($389)(4v pre-outs) same as the 3600 but in a 7inch screen
there might be a few specifics that I might have missed but when you decide which one you like I can get more in depth details..