After reading this post, I decided to try the Garage 1217 adapter, been listening on and off this weekend, works perfectly in my non-speedball Crack, no noises at all - it's completely quiet like the 12AU7. They shipped fast and the price was reasonable in my opinion for such a well-made adapter. Great service from Garage 1217!
Totally plug-and-play. I love being able to try out the 6SN7s.