Triode should be a more beautiful, open, clear, and detailed sound. The downside is that you will have less oomph in the sound. Even with efficient speakers, such as my Coincidents, the difference power makes is immediately noticeable.
When you listen in pentode, you'll have a lot more power (twice as much), and it will be a more straight ahead, rocking sound.
I disagree with triode being a smoother sound. But, it is a different sound. Again, the keyword is "beautiful", as that is what I equate triode with.
What does the rest of your system consist of, you should be able to hear the differences distinctly. But, I do believe it is common for us to have something going on in our systems where we are unable to hear differences that should be obvious. I was in this same situation for a while in my own system, finally breaking out of it late this spring. CD players, preamps, and cabling had no effect on the sound. One of the solutions was to ditch the preamp altogether, it was imposing its signature on the sound to the point where nothing else mattered.
