Search online for
downgrade Mac firmware
and see if it's possible to extract the firmware from the 10.6 disks (using Pacifist from CharlesSoft) then using a method to install the older firmware or not.
Make sure you make a bootable clone drive first in case it messes up.
It takes two reboots to have the firmware change get into NVRAM where it's loaded, so keep that in mind.
Thanks for the advice! There is actually a downloadable copy of the earlier version I'm looking for:
I downloaded this, and used pacifist to look at the contents... but I'm not sure what to do now. Any advice is appreciated!
Firmware only goes forward, if one bricks your machine Apple just replaces your logicboard or if they can't your out of luck.
However I've read stories/threads online it's possible to downgrade the firmware, but I don't know where I saw it.
This is the method to reinstall the firmware in case it gets lost out of NVRAM or botched update, but it won't downgrade it according to Apple.
So now you at least know how to reinstall the firmware, but I've read the downgrade can occur in place somehow.
Sorry I don't have any more information, you'll have to search the more geekier Mac hacking sites.
Ask on MacRumors.com, there are a lot of hackers there or can point you in the right direction if it exists.