1) Flash image.
2) Telnet to reciver.
3) Type: patchME 00 09 34 XX XX XX
Change: XX XX XX
To any walid hex value.
4) Reboot reciver to make bootloader changes to become active.
5) Telnet to reciver again, and check mac to be sure it changed.
6) Type: ifconfig |grep HW
7) If you have a valid DMM mac you should be able to use any image.

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Original DM500 have MAC like these...

00:09:34:20:xx:xx
00:09:34:21:xx:xx

xx:xx can be anything, but the 20 or 21 I think are very good to be sure to have a 100% good MAC address.