You did not mention which version of Magix Music Maker you are using, according to my knowledge not from Magix Music Maker version 17 but if you have older version first read their License copyrights etc.
Basically tracks composed by you could be sell, no need of Magix logo or credit.
If you look at the Soundpool DVD you will see Royalty free or without any license restriction. means you can use in your composition, you can not sale any loop from Music Maker or Soundpool as it is, it has to be used in your work.
For selling you work it is better to ask their terms and conditions with Catooh and other sites because some companies have their standard such as, audio should be in which format, what information should be included etc.
As copyright is very sensitive matter, you also ask the same question with Magix support and keep their reply in your record.