robzter
you should have 3 mixer output options
1, main out 1.0v (0db)output for phono type connections & 1.2v (+4db) for the xlr outputs which is balanced which basically means you can daisy chain amps with no loss in input volume between amps
2. record out (runs at a lower output than tha main out e.g 775mv + master volume has no effect on the output volume hence you can use this to lower the sound from the main out but have no effect on the volume of the recording taking place!
3, booth out (seperate volume probably on a dial type) generally used to connecting a another amp for monitoring
the denon dn-d4000 doent have the alpha track option like on the s3000 or 5000, 9000 models.
how good is the mp3 playback on the 4000, also i heard that the looping wasnt as easy to do as it was on the earlier dn-2500 cd player
hope this helps