Its Basically just an MC505 with a keyboard,it has some additional PCM memory and no D-Beam

,but other than that they are identical engine wise its just cosmetically different Obviously,its a pattern based machine aimed at dance,its sort of like the Quasimidi Raven in a sense(if you've ever used one of those)Similar to the ravens 8 track Sequencer for recording,Its easy to use and great as an Improvisational Tool,I sold mine to replace it with a JP8080,I kind of got bored with it but I regret it in a way,because they are becoming rather limited in numbers,and because of the way in which I work now It would have been a good asset in my working methods
I think Roland sold More MC505,than the 305,because its more of a Dance/DJ tool,whereby most people interested in it would perhaps not want the Keyboard aspect of it so opt for the table top 505,or would have alreayd bought the MC505 as the JX was released after it good buy if you can get one...but there seems to be less and less around,I'd like to get my hands on one again in the future
I recently saw one on Ebay,but never bothered bidding on it as it looked a scam,
You can read more info about it here
Roland JX-305
@Equinoxe5,not sure if Jarre used the Synth for recording,its never been listed on anything,but he certainly used the 505,(Metamorphoses)but he had a JX on stage at electronic night( though it wasn't switched on)