I fail to see why one would want to put things in the signal chain that makes things worse (distortion wise). I think introducing the "tube sound" is trying to address a problem that doesn't exist. With today's ultra low distortion DACs and Amps, you can peel away layers and get very close to the mix intended and heard in the studio. If you are not happy with this result, you should probably reconsider your speakers (ie upgrading, adding subs, addressing room nodes with dsp). Adding tubey distortion seems a very blunt and unsophisticated way to change the sound with unpredictable results. IMHO, going in the wrong direction, man.
I guess some people add salt and ketchup to every dish even at at a michelin star restaurant, and wear pink glasses going to an art museum...