I've been pokin into this issue for a few weeks too. 6 gb physical but Hardware Reserved is holding onto over 2gb.
One suggestion I found on the interweb was bent pins on the CPU socket causing this. (i7-Intel 920 CPU) I know...doesn't make sense. Except, I KNOW I bent some pins on my CPU when I installed it. (actually, the pins are on the MB.) Yeah, dropped the damn CPU onto the socket and bent 3 pins. I was almost shocked it booted up. Haven't had the inclination to actually tear it apart and try to straighten them out.
Did the msconfig thing too. That DID make 4 more CPU cores show up that weren't there before.
Memery Remap - no apparent option for this in Gigabyte BIOS