I got a some questions about this mod so I figure I'd answer them in this thread.
I don't think the mod takes away any gain. To my ears it has atleast as much. I don't run the preamp much higher than 5.5-6. Like I mentioned before the amp is still a 5150. Just now it's clearer and more open. Much of the fizziness associated with this amp is gone. I think that anyone who likes the 5150 will love this mod, but you have to like the 5150 in the first place. Hope that helps.
Jim