I have OS X 10.7.3 but Firmware updater says I need 10.6 to install update??

I have one of the original MacPros 1,1 2x266 currently running OS X 10.7.3. and indicating ROM Revision 3011. When I try to run this update, it fails saying I need OS X 10.6. Do I need the update (I presume yes since my ROM rev is lower), if so how can I install it??