Is a SUT needed?

@handymann
You might want to check the gain set up in your Theta - it is adjustable. Michael Fremer used 56db gain setting with the Dynavector XV1S when he tested the Theta, there is still another 20db available.

The use of an SUT is debatable - you might get a lower noise floor, but at the expense of other distortions that SUT's introduce such as phase anomalies and distortion, and another set of connections and leads that can only reduce transparency. I have many well regarded SUT's along with FET, Tube and Bipolar based MC step-ups/phono stages - SUT's (phase anomalies, slow and suck dynamics) & FETs (too coarse, grainy) belong in the department of last resorts.

Have you tried low noise NOS tubes from Andy @ Vintage Tube Services?

http://vintagetubeservices.com/

You might want to give him a call.

Thanks for the suggestions. I have my Rhea set at 62 on gain. Any higher and it overloads. Gain isn't the issue, noise floor is. Jperry has the the correct remedy I do believe. I'll call Andy about some tubes. I've spoken to him before-just wanted your opinions.                     Steve. 

@handymann 

I had a Rhea and at the 62 db gain setting you should not have a noise issue with the right tubes. I bought RCA tubes from Andy on his recommendation that fit in my budget and that took care of noise floor issues.

jperry:  I too purchased 4 matched RCA 12ax7's from Andy and my noise floor was reduced significantly. Still a little tube rush between songs at high level of playback, but that's just tubes.