Sound from speakers muffle mid song

Voice tracks are usually routed to the center channel. You don't mention having a center channel speaker hooked up. If this is the case, then you need to go into the receivers setup menu and set it for no center. This will reroute the voice tracks to your front speakers.

first off stock wiring for speakers,and or amp are with minimal wiring.Rewire system for better sound quality,also use noise suppresors if needed.

I think that rather than the mixer, that your front speakers may have a limiter built into the high frequncey amp. You may be asking them to do more that they are capable of.

after you play a cd while the cd is playing go into your audio settings and adjust theres settings foe each part on a stereo if u set the audio for AM//FM then play a cd the stereo changes to the cd settings

I have been recently using this Cd Dj deck at parties and have some general knowledge of the product, it has alot of potential. Is there anything in particular that you need help with? Or is it the general concept of using them.
Currently, i don't think there are that many websites that explain how to use the Cd decks, however i can provide you with some basic information. Most of the information here could be worked out by trial & error.
- Pitch control on the right of each cd deck can be slid up ( slows it down %) and slid down (speeding the track up %) i think the pitch control has a range of either +-10% or +-16%.

- Cue button, has the potential for Cue'ing or setting up the cd to instantly jump to the "cue'd" point with the press of this CUE button. This is done by either pressing play/pause button and rotating the jog wheel to a point of time in the track which automatically sets the cue point OR holding down the >> or << search button to find a spot within the track at a greater speed.

-Vinyl mode. Pressing this button will set the deck to the "vinyl mode" to simulate scratching or even backspins. pressing this button again will change the mode back.

- the Crossfader (or 'X' fader) button will select the left cd track if the x fader is all the way to the left and the right track if the x fader is all the way to right. having the X fader in the middle will play both tracks together.

- Low, Mid, High. These nobs on the middle section of the deck change the individual track by which it is corresponds. (Left side = left cd track, and vica versa) Low refers to the Bass of a track which can be essential for mixing two tracks and elminating excess bass noise. Mid refers to the drumming and even synth of a track, and changing this can result in some cool sounding effects. High refers to the 'high' frequencies of the track playing, such as snares, hi hats and possibly vocals. All these controls are crucial to understand in order to mix 2 songs together successfully. It's good to get a chance to muck around with these cointrols. The middle of each control resets the setting to normal or default.

- Channel fader. the two controls that slide up & down on both sides of the mixer on the deck. This is also referred to the volume setting. Useful for mixing seamlessly one track into another.

- Gain. This control at the top of the mixer refers to the volume level or 'gain' of the cd track that it corresponds to.

- Jog wheel. Serves 3 purposes. firstly it can be used whilst a song is playing to temporarily speed up or slow down the track to match with the song on the opposite side. secondly, whilst holding down the 'search' button, operates as a control to quickly find a spot in a song. and lastly when selecting "vinyl" mode, can simulate the reaction of a vinyl turntable. The scatch function, and backspin effect.

- The pitch button, is just another control to speed up or slow down a song temporarily whilst holding down the '+' or '-' button.

- Reverse button, for a certain amount of time will play the song on the left or right in reverse.

- Time. this button is essential to change the time selection on the cd deck, to either "Time elapsed", "Time remaining" and "total time remaining on the cd".

- the "tap" button, allows the user to physically "tap" the button in time with the song's beat, which calculates the Beats per Minute (Bpm) of that song. which is essential to work out the bpm of 1 track to mix the speed with that of the opposite deck.

- Cd/usb/sd, changes the mode of system reading. from CD to USB or SD card.

I really hope this general guide to using the Audioline ProDJ MDex3 has helped!
Peace. Marc.

5.1 plays surround sound tracks when available, when playing an audio track that was recorded in stereo (2 channel) it should only emit from the front left and right speaker, and when playing a movie in 5.1 at points in the audio track all five speakers should emit sound. Is this the case?

I had exactly the same problem and followed the OP's solution, which worked, but I couldn't hear the track as it was being recorded.  So I tweaked the solution.  If you do the following, you don't have to keep changing System Preferences as you switch from record to listening:
Go to System Preferences, press the Sound icon, and click on "Sound Effects."  Then select the drop down menu and select "Play alerts and sound effects through selected sound output device" rather than the USB choice.  Then click on "Output" and select how you want to listen; I used speakers so I selected "Headphones" where the port is "Built-in audio."  Then click on "Input" and select the USB choice.  Now record a track and you can hear it being recorded through your speakers (or headphones).  When it's done recording and after the software transfers it to iTunes, you can play it again through your speakers without going to the preferences panel.  

Say "sound card" or maybe you fryed something due to overuse and or playing them too loud? Nah. Everyone plays speakers at the recomended level. Seriously, you need to get this checked out: radioshack.

have you used the mic input connection as this is used to split the channels

First thing you wanna do is to try another set of headphones. If it still sounds muffled then theres a fault in the audio output section and these things are non user serviceable. Your gonna need to send back to the manufacturer. Good Luck