I am quite familiar with the Marantz 3300/3600/3800 preamps, and owned a Marantz Model 7 tube preamp for nearly 30 years. I also owned a Hafler preamp.
A new Schiit Saga blows all of them out of the park sonically. I use a Sylvania Bad Boy 6SN7GT in the original Saga and the sound is great.
why not build a system out of new Schiit gear? And if you want a complete system without tubes, the Schiit Ragnerak is on closeout at $999. You can put a multibit DAC in it for a few hundred more, and you get a headphone amp that ranks up there with the best as well.