The 9xx tracker command (set sample offset) is not supported in the first version of the player. Implementing the command like it's normally done in Amiga and PC players is not possible, because it's not possible to change the PCM wave start offset on the OPL4 without switching the chip to "memory write" mode, which also disables sound reproduction. It seems that the only practical way to implement the 9xx command is to have the converter automatically create a separate sample/instrument for every (sample, 9xx offset) combination. Even then, you could only have a very limited number of different 9xx offsets in the same song, because the OPL4 only allows 128 different custom samples.