I used an Onkyo amp for months. Then it died. I replaced it with a Denon. The difference was easily heard. Same source, same speakers, same positions. The Denon had deeper, cleaner bass and more defined high end.
Tube amps sound different than solid state, but I would not say they sound better. Back in the day, the best amps were big bulky tube amps. I think people who grew up with this sound became snobs and now prefer that sound, not because it is better, but it is what they learned to hear. With the improvements in speakers and amplifiers, you no longer need to throw power at them to get good sound. I think it is like Coke and Pepsi. Neither is really better, but some like one over the other. That is how it is supposed to work. I personally believe solid state better recreates chamber music. The instruments sound more live. The tube amps better reproduce electronic music, which usually has intentional warm distortion.
It is much like fine wine. Some are noticeably better than others, but the more upscale you go, the more subtle the difference. There is little difference between a $20,000 and a $40,000 audio system. Most people could not hear any difference; or taste any difference between a $200 and $400 bottle of wine, Good enough is good enough. Don't chase an ideal. Chase the sound you like.