I wouldn't go for the Scanner chip at first. Moreover I would go for stuck keys (spring problems). I often get those errors on my two Emax I when I take a while since I don't play them.
Same symptoms: Notes sound bit after depressing keys, double triggers sometimes, etc etc.
When depressing the keys several times, things start to run fine for a while.
I would try to replace the key springs (Ebay provides you sellers with that stuff). Just in case this method don't work, I would go for the Rockwell scanner chip. As Jammie pointed before, an expensive one.
Best..
DX5.