Hey Jonny,
Sorry to hear that you're having problems. Did you measure the
delay? 2-5 milliseconds seems awfully small and well within the
typical latency between simultaneously triggered midi events. If
you're perceiving latency, either you're particularly sensitive to
timing errors or the latency is much greater.
Software sequencers, effects, and instruments can approach--or maybe
even attain--sample accuracy with internal midi messages, the hardware
midi spec (being serial) basically has a minimum 2 msec latency
between any 2 midi events. Maybe you find your SE-1 somewhat sloppy
compared to software instruments?
Or maybe the timing errors are large. Could be the cable, the
controller, the sequencer, the midi interface, the midi interface
drivers, etc. Could be as you fear: the unit has a defect.
Tell us about your set up in detail. How are you using your SE-1?
And with what?