. . . . However, is there any commercial restrictions on using soly your own royalty free loops like the ones from www.producerplanet.com? . . . .
ProducerPlanet also belongs to Magix and is the source of additional soundloops, instruments etc that Music Maker and other Magix programs use, they are covered by the same licensing requirements, as detailed here.
Do note the following:
Royalty free does not mean they are licence free - it means you do not have to pay a Royalty to the creator of the loop etc, often based on the number of plays - eg on Youtube, radio etc. and is in addition to any licencing conditions.
Copyright - this still belongs to Magix, you never own copyright of the sound pools, loops et, you are only allowed to use them within the terms and conditions of the appropriate licence.
The same applies to any audio which does not specifically say 'Free to use' eg under the Wiki Commons licencing system.