the aux line is an analog input, not digital or midi related

Yes, sir. I know that Mic2/Aux is an analog input but I think that when the system is not in thru-mode the signal will normally go to the software and then back to the board. What I'm wondering here is that could it be possible to route the SP6 output to this channel so that the Mic2/Aux volume knob would act as volume controller for the whole SP6.

i thought it was an Aux Input not Aux Ouput?

Yes it is ;)

The purpose of this feature is to be a back up line. If it was mappable it would loose its intention, it is an analog input or out put, can not be used on this controller, other controllers might offer a hybrid line. On the ddj-s1 Its phisically dettached from the midi system. In another words if you umpluged the usb cable, the signal still goes thru as a bypass if you are using the power adapter. The reason is because the mixer only detects the origin of the signal to make a recording of the mix. Like I said it is not phisically posible to use it as digital source. Take a look at the ns6, it offers the option to use as an stand alone mixer and has phisically the option to move from midi to aux line.
Im Just trying to help.
Greetings man

Maviccf, thank you for a very good and specific answer! ;)

Your welcome
Enjoy 2.0 :D

I have a Pioneer ddj s1. I'm trying the aux in but it doesn't work. I want to record something through the aux in with serato itch. Can somebody help me???