Battlefront and Battlefront II each had an Update to install alongside the DLC. The original 2nd installer (update) wont work on a Jtag/RGH even with the modified compatibility partition. What I CAN do is put out an update just for homebrew consoles like for Halo 2, Mechassault 1 and 2, Splinter Cell etc.
I'll work on that tonight or tomorrow. I can not guarantee it will fix your problem, as 360 emulation of Xbox is EXTREMELY spotty at best. If you want better emulation your best bet is asking around the 360 scene. So I understand your frustration, but I do not have a hand in 360 emulation, I will do what I can to help from the content end, but I can't do anything to help fix 360 emulation.
EDIT: Just to be clear. The "JTAG" updates I've released only install what the second (update) installers normally would from the older DLC installers. You still have to run the first (DLC) installer to get any actual DLC.