Preamp match for my First Watt F-7 amp.

There is a Supratek Syrah on US Audiomart that would do the trick if you can convince him to ship or make arrangements to pick it up.  Has gain of 26db at max setting.

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

With 90db speakers the 18db gain from the Quicksilver line stage should be more than enough to drive the First Watt amp as loud as you can stand.  I suggest you check your connections especially the output level on the Audiolab streamer.