Getting the best sound quality when recording in traktor with an external mixer?

I've been working on trying to get the best quality recordings using a djm-707 and an audio 10. How I have my levels set up is I started by playing two loud songs at the same time and set the main a little under clipping at -6.5. I feel that should give me the best clean signal going into the mixer. I then set channel levels so that the songs peak at 0 on the channel volume meters. I noticed that the booth out has the same gain structure as the master, so I set it to the 3 o'clock position, which is where the master peaks at around -1. I then set the recording knob in traktor at +10 which is just under where it peaks into the red. So assuming all my levels are just under red that should give me the best sound quality no?

I recorded a mix and found the overall volume of the recording to be surprisingly low. I turned up the volume of the channel that I was playing it on and it sounded ok. Should I be satisfied, or should I ignore the red peaks in traktors recorder and record at +11 or +12? What do you guys with 707s/909s have yours set at?

Also, I've been setting the gain of each song to peak at 0, but I've noticed that in my recordings that some songs still play louder than others. I'm assuming that this has to do with the amount of compression that the producers have given to each song and while the peaks are the same, the rms varies. Should I be setting my peaks at around -3 on the louder songs and 0 on the quieter ones to help even this out?

Another thing I have noticed is that when I turn on the fx send/return on the mixer, the volume gets quieter. I set a loop from the from the outs/ins and noticed no change, so imagine the difference comes from the audio being converted from analogue to digital and back to analogue. Has anyone else noticed this?