first of all, i forgot, the midjay does have arranger a, b, c, d, intro and break butotn- sorry.
Basically many of the main features found on an sd3 are on the midjay+, but it is limited only in that the unit is primarily a multimedia player. That means the emphasis is on playback and editing of Midi, Mp3 , Wav and SFX files and lyrics. However, styles and sounds are there but not so easy to bring up in real time. Sounds can be edited in the same way as an SD3 (4 voice editing). Style editing is very limited though and you are essentially stuck with the factory styles.
An arranger is designed for real time use and the SD3/Audya 4 have all the small things that make using an arranger for different types of people possible - virtually every performer uses these instruments in a different way and Ketron have built in almost every possible permeation of use on the arrangers.
For live use, you generally need quick access to levels, styles, sounds etc. This cannot be achieved in the same way on a midjay+...but, if you operate entirely from a master controller or pre-program your entire setlist - as some do, then you could get away with a midjay. You just have to accept that it will be limited in operation.
I suggest you scan through the owners manuals of the various instruments to see what is possible and what is not.http://www.ketron.it/index.php?option=co...20&lang=eng