@LoadWB
AE3 does not use any licensing scheme. Although there used to be an upgrade price when AE4 was sold by Computer City for 149 euro, the 100 euro drop in price also means that there is no special upgrading pricing from AE3 to AE4 anymore. Frankly, AE3 was also released around 10+ years ago I think, so I would call that fair.
Re: MIDI support
Please keep in mind that AE4 for OS4/AROS/MorphOS is not the same as AE5 for Windows/OSX. This means that the features you find on the main page of the Audio Evolution website are for AE5. AE4 is audio recording only and can only sync the start of playback to MIDI through CAMD, although this has not been tested under MorphOS.
I hope this explains a bit. Feel free to ask any more questions you may have.