Tube Preamp with adjustable gain

Supratek preamps also have adjustable gain.

The New Eastern Electric Avant preamp has adjustable gain.

some photos here at 6moons when the DAC was reviewed.
http://www.6moons.com/audioreviews/easternelectric/dac_2.html

Disclaimer: I am the North American distributor for Eastern Electric.

all Joule-Electra preamps have adjustable gain from 0 to 17 dB ( by change jumpers, extremely easy)

As mentioned above some of the earlier ARC preamps have adjustable gain. I used to own the LS-26 (now discontinued and superceded by the LS-27). The LS-26 is an excellent preamp and has three gain settings that you can select via the remote control. So no need to open up the case and mess with jumpers. You did not mention budget by the way. What's your upper limit?

Used Music Reference RM-5.