I've just used MIDIOX to pull the patches out of my Poly-800 II; in so doing I discovered that the 4th byte in the string should be 0C not 01 as it is said to be for the Mark I and EX. FYR the whole thing is

F0 42 21 0C 10 F7

If you get it wrong the machine gently tells you

F0 42 21 0C 20 F7

Hope this will help some folks.mn