If I can pop in to contribute a bit to this, I recently purchased Music Maker (trying Standard then Premium) which was great, and although I had to learn how to use it [I have never used any MAGIX products before], I had a lot of fun with it. I switched to Samplitude Music Studio (after finding it would suit my personal needs better and am now learning the nuances of that. I have also used ACID Products in the past (when it was owned by Sony before MAGIX) and so I can add a bit of the differences with that too... To briefly explain some differences, simplified:

In Music Maker, it seems to be [to me] geared more towards taking the pre-made "Samples" (pieces of music or sounds) and place them how to you want, adjusting their Pitch (high or low sound) and adding Effects to them, to create your songs. Coming with a huge amount of samples, you can purchase additional sound samples (from MAGIX or anywhere else really) and use them, as well.

"Instruments" (VST’s) are available in two types it seems: synthesized ("computer generated sounds") and some Instruments that use ‘samples of real sounds’ as well in them as well (as sources to create the audio), but you can't just drag-and-drop Instruments into the Arranger [from what I’ve seen], you have to make MIDI Objects, which are essentially "blueprints for when the sounds should play and at what notes/pitch". Telling the Instruments when to play what note is how you begin using Instruments, adding effects and other tweaks afterward (in general), from what I’ve seen so far.

The Samplitude line of products [in my experience so far] offers more capability and personalization in the composition of a song, using more MIDI objects and requiring more “exactness” and technical arrangement, rather than using mainly pre-made sound samples (although you can definitely use them in the arrangement of a track in Samplitude, it just seems that Music Maker is targeted more towards using sound samples and quickly putting them together in the making of a song, with many tools that make it easier and quicker, compared to the Samplitude line).

Samplitude seems to be geared more towards artists that would play RealLife instruments and record them into the software, then editing the recordings and adding effects. The addition of VSTi “Instruments” and the ability to use sound samples as well, all add to the complexity and possibilities that the Samplitude line seems geared towards, increasing in capability as you go up into the higher products. Personally, the highest-tier Samplitude products are out of my league (and needs), but for an aspiring or Professional Producer of music, the top end software seems quite capable for what they would be wanting to accomplish.

To mention ACID Music Studio / ACID Pro for a moment, were originally developed by Sonic Foundry, and the little that I saw of it it back then, it seemed to be geared mainly towards use with Sound Samples, making it easy to place them and changing their pitch easily work them into the creation of a song. However, ACID has been developed beyond that now, seeming to have the same goals as Samplitude in mind, because it can not only use Sound Samples, but also utilize MIDI Objects (assigning “Instruments” to the tracks and telling the Instruments when to play what note), still with the capability to add effects and other mastering afterward, of course. If I had to summarize what the ACID line is like, I would say it is a combination/between of the Music Maker line and the Samplitude line, being closer to the Samplitude line of products.

I am new to MAGIX Products, but the above is what I have learned to this point, experimenting with their music software. I am enjoying it... as well as the helpfulness of this site! I wish you well in your endeavours.

~M