I'm testing several Linux flavors on a Sun-Fire-T2000 server with System Firmware 6.7.4.
I have tested several Sparc64 linux distributions, and only Debian 5 (Linux 2.6.26) and Ubuntu Gutsy (2.6.22) boot over network (TFTP), rest of tested systems fails to ok prompt when loading kernel (before Linux execution) with error: "/packages/obp-tftp: Last Trap: Fast Data Access MMU Miss".
That's not the least bit surprising.
There are versions of Solaris 10 and OpenSolaris that won't function on the UltraSPARC T1 CMT architecture, either.
I don't think there is anything you can do to tweak the OS's you have currently chosen to investigate. However, that would be a discussion that is better suited in some sort of Linux forum. Rewriting a kernel is outside the scope of the Hardware Forums.