Which version of Music Maker you use is not a factor in what you can and cannot do regarding music containing Sounpool material.
To be concise - if you use any part of any of the Soundpools then you have to purchase the Pro licences, for every soundpool used from Catooh.
Note 1 - these are licences to use for commercial gain - you never own the copyright to the soundpool music and cannot claim copyright to them in your composition.
Any music you create using the synthesizers, that you compose and play yourself, are yours to do what you want with, with the provision that you are not ripping off someone elses work, riffs etc. You can claim copyright to these parts only.
Note 2 - if you are thinking of using Youtube and the like for selling, then you are likely to have claims for copyright infringement on those soundpool parts that are used from other people.
With the likes of Youtube you have to agree that you own copyright of the entire creation when in fact you don't - you and any other person who has used Magix sounpools only have a licence to use them. This unfortunately is something that Youtube and others do not seem to comprehend.
. . . . So If my songs only use virtual instruments (midi w/ effects + synths) but don't use anything from soundpools AT ALL, . . .
That is correct, with one exception - the default instument / synthesizer music, with the exception of the drum engines ( the drum engines are too generic to copyright), is copyright Magix.
You must create something new using the instruments / synthesizers - however you do have to be aware that anything you compose must not be a riff, distinctive note sequence, etc, that has already been used commercially or is from music that is still in copyright.