To combine your questions:
Yes your board is a Xenon one.
Yes it's possible that it's been send to MS for a faulty DVD unit, and got replaced with a Liteon.
No you can't play ISO's from a external HDD without a ODDE.
jTAG is dead since 8xxx
RGH can work on a Xenon but personally it's not worth the trouble.
You can flash the DVD drive.
That + I'd like to continue this here
Hi could you please Make a guide for Burning ISOs or playing on a External HDD using ODDE to play on the x360 safely with minimal possibibilities off getting Banned from XBLA?