I factory-defaulted an FX7500 and here are the only options it asks for (via a DHCP DISCOVER captured with Wireshark on Windows 2012 R2):
FX7500 firmware 1.2.84 & 2.3.23
OPTION 1: Subnet Mask
OPTION 2: Time Offset
OPTION 3: Router
OPTION 6: Domain Name Server
OPTION 12: Host Name
OPTION 15: Domain Name
OPTION 28: Broadcast Address
NOTE ON OPTION 12:
Specifying option 12 does not work in these versions of code--the reader sends a request for its default host name and/or doesn't listen to the offered option from the DHCP server.
We have requested changes to the code to allow changing the hostname, but it has not been implemented.