I have tried on two different computers and both have the same result, the audio recording plays back slower for my voice than what is playing for the music.
What are the sound cards that you are using on these computers?
What is the sample rate of the song?
What is the sample rate of the recorded voice?
Sample rate is the key here, unless there is some issue with the sound card or recording device itself. I think by default, MAGIX records at CD quality. This would have a sample rate of 44100 Hz with a bit depth of 16 bit. To get a better understanding of sample rates, you might try googling "Audio Sample Rates" to see how others describe it.
For the most part, 16 bit, 44100 Hz is what all audio would translate, if it was recorded directly from MAGIX... that is unless different specifications were applied.
If you record your voice at one sample rate, but the playback of the music in this case is at a different sample rate, then there would be either a faster or slower sound to the recording, this depending if the sample rate was higher or lower than the source rate in the music.
It does get very confusing, scientific, and mathmatical as everything that is digital is math. So, the best thing to do here is check what the sample rates are, and make sure they match... but if possible, make them 16 bit, 44.1 kHz so they can easily be burn to CD without the same issue.
The other issue is the sound card... an actual sound card, not a integrated sound chip can support many different options on playing back while recording as it has built in resources for this process. Sound chips are great for recording or playing back, but when asked to do both at the same time, they try, but often fail.
I hope this helps in some way. I do not know which version of Music Maker you have, so i am unsure how to provide you with information on checking to see what the sample rates are of the material.