Live swap from cdj to S4???
Hey a very noob question i have read lots of threads but could not find the exact answer.
It is just with a live cross over from one dj on cdj/turntables and when im on after with my S4 i dont wanna stop the music. It surely a very simple answer help would be appreciated.
Your S4 would be plugged to a different channel on the clubs mixer. Use that to to mix into his track then leave that channel full and swap to your S4.
Voila 
ok so my 2 RCA’s can go into one side of the djm 800 mixer master. And just mix out from the other dj? sorry for stupid questions.
Depends if it’s a 2 channel or 4 channel mixer.
If it’s a 4 he plays out out 2 channels you plug into either of the free ones then just fade using that (your channel) into his mix.
If it’s a 2 channel when he drops his last track you will have to unplug the dead channel then plug your S4 into that.
Hope that helped
S4 out to one channel on the clubs mixer. When the DJ before you is done you mix into his song and then keep going from there on the S4. You don’t need to do anything with the club mixer other than the initial hook up to the one channel.
I’m assuming you mix internally? In which case, since you only need one channel on the mixer, run your stereo RCA cable (1x red and white) to a free channel on the back of the mixer. If they’re all full, wait til the last DJ is on his last record on one of the CDJs and unplug an unused one. Then mix in with that channel.
I feel an echo 
haha, great minds.
Thanks everyone for your help will feel better when walking into the club..
This is the exact reason why i embraced the S4, so i didn’t have to mess around with 4 pairs or RCA’s and start unplugging loads of stuff.
The S4 is an easy setup!