hi gja,
so the firmware is model-specific...
is not possible to use the 1.60 fw from bdp8000 for your 7500

in this way, your player wont detect anything...

also for the UPG or UPG_all thing, please do not rename the file, since this may bring corruption as well.
UPG= upgrade
UPG_ALL= upgrade all

if changing UPG_ALL to UPG, some part may not be upgraded for example the loader.

are you able to get the latest firmware for your BDP7500? what version are you using?