I would go find a s900 and really try one first hand to see if the MFD feature is really what you need if your not a proficient Arranger KB player....judging by what your describing I dont think so & an expensive mistake. If your going to play fiddle, guitar, vocals against the music.....do the children play also?
I might think of going a different way there are alternatives.

Look into teh ketron Midjay or try to find a Roland Discover 5 MODULE
http://www.ketronus.com/midjay.php

http://namm.harmony-central.com/SNAMM03/Content/Roland/PR/DisCover-5M.html




[This message has been edited by Dnj (edited 11-25-2008).]