I'm a little perplexed as to why you would procure Movie Edit just for a synthesizer as opposed to having Music Maker. I'm also not sure where this synthesizer option you're talking about is located in Movie Edit.
However, if you load a wave file into the timeline and then right click it, (or Alt + z) you will see an option "Edit wave externally." This will bring you to a sub-program called Magix Music Editor. (Not to be mistaken with Magix Music Maker.)
In Music Editor there are various options for working with sound files with equalizers and noise reduction filters, including some echo effects. But the program is really more tailored to fixing and cleaning audio problems as opposed to rendering and enhancing sound tracks. I don't use it all that often because I do most of my audio rendering with Music Maker and try to avoid the need for cleaning and noise reduction as such filters tend to sabotage the quality of the sound file.