martin-anderson, your speakers did not magically change their character, that is in relation to other speakers. All speakers can be changed as dramatically as yours. Audiophiles think they have done something particularly wonderful by pairing a more suitable amp. You can do that with any speaker. The precise same degree of change is available to any speaker. It’s not unique to your current one.
You have demonstrated the fact that everyone who argues that speakers are "easy to drive", thus a lower powered amp is sufficient, is literally directing you to achieve poorer performance in several parameters of sound quality. It’s a good thing you didn’t listen to them and tried a more powerful amp. My guess is that you also don’t sense more distortion, but less. Your speakers were being driven weakly, so the bass was insipid, the soundstage not great, and the tonality poorer. Now, you have a more balanced sounding speaker.
I use the Legacy Audio i.V4 Ultra Amplifier following the review at Dagogo.com on all speakers, even the very efficient PureAudioProject Quintet15 Horn (reviewed). You bet I put 600wpc on that speaker because it seems like a completely different experience than some pissy 100W tube amp. I have zero interest in such pathetic amplification, which is also noisier than the Legacy amp. Want a downgraded experience? Feel free to go that route. Lower power tube lovers think they’re genius, but they are hearing insipid sound. Whatever.
In regards to pairing your tube amp with easy to drive speaker and subs, you’ll have that same huge spectrum of performance available. There is no assurance that with any given speaker you will love the result. You very likely would have to make a bunch of changes to that rig to optimize it. That’s the way it goes in system building, but it’s fun and worth the effort when you find ideal combinations of gear.
Bottom line: Your desire to use smaller speakers with subs very likely would cause you to lose attributes of larger speaker systems that you would not be able to recreate, and the amp matching would not bring them to you. Feel free to message me to continue discussion, as I currently have the Wharfedale Opus 2-M2 set up with Legacy Audio XTREME XD Subs (all reviewed) in a comparison to the King Sound King III electrostatic speaker. When switching between them the attributes of each system are striking.
Keep trying things. You will begin to have your eyes opened to the vastness of the performance spectrum - for any speaker.