Tube amplifiers are archaic 1950’s technology. Expensive tube amplifiers are a very interesting animal indeed. You are literally paying money for distortion. The tube sound is just distortion that just so happens to have the correct harmonics to “sound smooth”. So if you want to spend money for an amplifier that literally produces 10-100x more distortion than an equivalent solid state amp be my guest. Many people indeed do like the sound. However with DSP you could create that exact sound cheaper with a solid state voltage amplifier.
I would recommend this for a 4 channel amplifier.
http://www.zapco.com/prod/comp_prods/c2k25Frame.htm