If you had access to a larger DMX controller you might be able to determine (1) how many channels the unknown fixtures use (2) what the actual channel lineup is. I never assume anything when it comes to fixtures without a manual (or at least a dmx chart) because I have come across just about every possible combination, including blank channels in the middle of a block.
The fixtures could have a master dim channel that has to be set at full, or a strobe channel that has to be at full. The first channel could be a "control" channel, or a master dim channel.
Sometimes it's easier just to walk away.
