Amplifier for Sonus Faber Extrema


I´ve just bought a pair of Sonus Faber Extrema Loudspeakers and I want to buy an amplifier for them (used).
My actual system: Krell Kps20i CD Player, Sonic Frontiers Line 2 SE Preamplifier, Classé Audio Fifteen Power Amplifier and Audioquest Volcano DBS Speaker cables (biwire).
I want to replace and upgrade only the amplifier and I want to still use the Sonic Frontiers because I love this tube preamplifier. So I´m loocking for an amplifier to use with the Extremas and the Sonic Frontiers.
Some options could be: Classé CAM350 Monoblocks, Krell KSA300S or Pass X250.5
I will apreciate all your suggests and recomendations.
elduende14
I am currently Bi-Amping my Sonus Faber Extremas with a pair of Threshold SA/1 mono blocks on the bottom end . And a pair of Threshold SA/2 mono blocks on the top end and loving it !

Stick with pure class A sound amps for the Extremas. And I suggest Bi-Amping if you can do it. It brings the Extrema's to another strosphere when Bi-Amping with the right amps.
Mark Levinson 20.6 are awesome amps. But there pure Class A. There gonna get hot and your electric bill will feel it.

I would recommend Levinson 23.5 or Mccormack DNA 500