You can do that but it still doesn't sound the same as a zero feedback tube amp that has a true matching output impedance. I know because I've had both & made my own impedance matching networks for transistor amps in order to drive horns & while it did improve the sound over the original transistor sound the zero feedback tubes still had the sound to die for even though the output impedance was matched on both with the output network on the transistor amp. Even the output power was matched with the tube amp with the impedance matching network on the tranny amp, 25 Watts /channel to the speaker. By the way the tranny amp still neded to have a resistor network across the terminals at the back of the amp as well as the resistors in series with the speaker to sound it's best with the Altec Lansing Voice Of The Theatre A7-500 that I had at the time. This in part hid the reactance of the speaker from the amp Which was an Adcom GFA 545 which was modified. I had used it to drive many other speakers before, even some as low 2ohms & is sounded great on them but really needed the impedance matching network to sound it's best on the horns even though the load was an easy load for the amp. The easiest load that amp has ever seen with me.
Of coarse this does not apply to headphones, They should be driven with the output impedance that they were designed with originally & not make assumptions that we know best how to drive them without consulting the manufacturer.
Out of interest, would you be able to elaborate in technical terms why the tube amp behaved better? Or is it simply an observation?