Amongst my minions I have a Z1, that I am using with Cubase.
The synthesizer is old, but there should be no problems using it with MIDI. What kind of a MIDI interface are you using now? What kind of MIDI cables are you using? Are the cables old, or long, etc.
MIDI is simple (I mean to utilize it, hardware wise and software wise) so there is no reason for your experience, other than typical issues. E.g. Just like MIDI is easy, it is also slow. The longer cables you use, the longer the MIDI messages takes to reach its destination. Older or inferior (though you do NOT need expensive) cables will affect quality of transport, and since MIDI is digital there is no “distortion” per se, but missed messages, on the receiving side.
Do you have a way to test another MIDI device (synth or otherwise) with your current interface? Do you have the ability to test a shorter, newer or a “thicker” MIDI cable?
/E