The GPXE NIC listing gives you two choices from the Realtek family to boot from.
However, if you got the we announce ourselves to the router message you have obviously PXE booted!
So now via webadmin from your Core you can check to see if a MD was created under Media Directors, or,
from the command line look at usr/pluto/diskless directory to see if you have a number there.
PLEASE NOTE: If you have a core/hybrid there will be a number associated with the Core MD.
If you have a CORE/Hybrid and a second MD you will have 2 numbers. A Standalone Core + separate MD = 1 number in diskless directory.
If you have MD in diskless directory for your new MD and webadmin show a MD entry in media directors then you have a possible architecture mixmatch.
What is the type of cpu for the MD? Intel? AMD? 32-bit/64 bit?
Your MD problem could also be related to your default display setting.
There's a start.