The use of a tube line stage into a solid state amp is sometimes an unpredictable hit or miss gamble. Even if the output impedance of the tube line stage is low enough, or the input impedance of the amp is high enough for a theoretical match (e.g., amp impedance is at least ten times the output impedance of the line stage), the sonic result may not be that good. This is not a common event, but, it is a risk. I've heard several occasions when there was such an incompatibility resulting in a dull, lifeless and muffled sound.
Also, to really get the benefit of what tubes can do for the sound, one should really start with a tube integrated amp or a tube power amplifier. It is in the actual driving of the speaker that the benefits of tubes really become evident. But, it is also where you can run into problems with the sound. I would start with looking for the right tube amp, not the right tube line stage first, to get into tube sound.