While I am partial to NAT Audio since my firm also imports the line, I would like to suggest doing some research on Plasma R or the Symmetrical preamps which will easily outperform the linestages mentioned above and the Plasma R has 10 tubes inside while the Symmetrical is configured with 12 tubes.
www.nataudio.com and www.musicalsounds.us
Good luck
www.nataudio.com and www.musicalsounds.us
Good luck