I don't know about the dx9 but the tx81z manual contains tables of the memory layout of the voice banks. Some bytes contain more than one parameter, so you really need that info, which is probably in the manual.
The first thing i did when decoding the voice bank layout was looking for the patch names (ascii chars, 41h to 7Ah).
I wrote the sysex bank as hex string, threw it into Excel and made a map for each voice like this (each colour represents a parameter group, yellow = op1, orange=op2, and so on) just to get my head around it..