Okay, where do we start. I will begin by telling you the differences between line level (line out), headphone out, and phono out... because without knowing those basics nothing I say will mean shit to you. Honestly, I am really fighting against telling you to do some f-ing reading on google and your gear manuals. In fact right now I wish BG saw this first.
Line level - that is the audio output comming from line outs... you can NOT plug outputs into outputs... outputs go only into inputs... so the audio output from your video game or DVD player does NOT go into your TV's audio output. Sure, the RCA cables will physically fit in the jacks but nothing will happen. your mixer will have a "LINE IN" that is either RCA or quarter inch. Your MPC has a line in also (RECORD IN)... you can run the left and right (red and white) RCA jacks from the dvd player directly into your MPC by getting these:
Headphone out - this is not line out, it is a slightly amplified signal where as line out is not. The reason the signal on headphone outputs are slightly amplified is because headphones require that little bit of power for them to work. You can physically connect the headphone output from your ipod or tv to a line input with adapter cables but if you can avoid it I suggest doing so because the signal current is higher then line level and has more of a tendency to distort.
Phono - this is the common signal from turntables and record players. Tables require more power then line level (line out) but physically you can connect a turntable to a line in... however it will sound hollow and shitty as well as it will be lower volume when done. That is because turntables require a phono input like on your DJ mixer. That in a sense "converts" the signal to line level.
remember, outputs get connected to inputs... the output from your dvd player wont accomplish anything when connected to the output of your tv or mixer...
never mind the television. get two of the things like in the picture I posted and attach them to the end of your RCA red and white jacks from the dvd player and plug it into your mpc. the yellow one as you normally would should get plugged into the yellow video input on the tv so you can see what you are clicking with the remote.
I try not to spoon feed anyone, but once in a while I make an exception.