its read only,
on 1.0-1.5 xboxes the tsop is eeprom flashable because it is "Electrically Erasable Programmable Read Only Memory" stored on the Tsop "Thin Small Outline Package" (so its technically an eeprom tsop)
Obviously there is also a chip that we call the eeprom. This is on all versions. And that stores the drive info.
so where as the eeprom is known as the eeprom. the tsop is also a eeprom but because its on a tsop chip we call it a tsop.
the 1.6 does have an eeprom which obviously is re writable due to it being Electrically Erasable Programmable Read Only Memory which also stores drive data, but the 1.6 does not have a Tsop chip that holds the bios.
the bios is instead stored on a diferent chip. which is Not an eeprom compliant chip, so its read only..
because its not erasable you cant flash it.
should have answerd your question.