I used the Primaluna EVO 400 pre and amp for a year with the Forte IVs, that didn’t go well..seemed a little harsh and lean. I tried a lot of different tubes from 1960s Mullards and much more, didn’t help. Now I am using the Pass Labs XA-25 and Pass XP-12 preamp, that sounds the best with my Forte IVs and the Volti Razz I have. When my Pass Labs dealer gets back to me going to try the First Watt Sit-4, and see what’s happens..