Hi mike,
I found a very old version of that jtag emulator, it has some 74HC series chip instead of that CPLD. That explains its function I guess. Then why it is ommited in the on-board emulator? For versatility? You know that JTAG probe is expected to program various TI products, whereas in on-board stick it only programs the chip that it is connected to... Therefore I am inclined to follow the on-board case. So far I could not found much documentation on that. Actually I dont know what to decide.