I'm considering the single-ended FM-155 to go along with the Symphonic-Line Kraft amp.Coincidentally, I used an identical combo some years ago: a stereo Kraft with a 155 & later a 266. Both with excellent results, better than the RG3 & the tube one. The FM is hyper detailed and the Kraft is (reportedly) wide-bandwidth, so all is fine. I didn't find it cool -- but then my whole system isn't very cool anyway; it's on the warm side of neutral (i.e. 100Hz is higher than 10kHz). As a matter of fact, I slightly preferred the little 155 (but the reason is probably psychological).
Other pre's that did well with Symphonics are the old Goldmunds, and the CATs.