Preamp match for my First Watt F-7 amp.

I cannot think of any situation where that much gain would be exhausted before one hits a level that would cause any amp to clip 

I was thinking the same thing. Is the preamp getting enough voltage? 

I have an F5 and a J2. So I’m in the low gain club also.  I run an Aric Audio Motherlode II in my main system,and his Unlimited gets in the rotation downstairs. His preamps have adjustable gain,which really works out great with low gain amps,and high gain amps.  The Supratek that’s been mentioned earlier will also suit your needs.  

Don sachs with adjustable gain. What a guy!

Don only makes one model now with a fixed gain of 18db

I feed a FirstWatt F8 from a Van Alstine Transcendence RB 10 preamp. I rarely have the volume control past 10 o'clock. The sound out of Focal Aria 906's, rated 89.5 dB sensitivity, is terrific.