Hi.
I've had a look around and my own 4000DS user manual (pdf) makes no mention at all of a 50Hz only version. Neither can I find anything different on the web. However, a service manual in pdf is available here:
http://www.audiocircuit.com/index.ph...=4000-DS%20Mk2 which does mention EEC models (50Hz), but whether it'll be any use to you remains to be seen.
Good luck,
Roger.