Sorry I can't help with your specific question and don't mean to start a debate, but have you considered a passive preamp as an option? I'm also seriously considering to upgrade my preamp and been reading up on the pros and cons of passive vs. active and like to hear why folks, particularly the ones who are planning to upgrade, don't consider the passive route more often. Please ignore this post if it's taken as hijacking the OP's question.
P.S. I mean something like FW B1 or similar.