The two most common mistakes are bass and treble

I kind of would really like to hear @atmasphere and Fritz in a room together sometime. I think that would potentially be a phenomenal match up.

Yes it is a nice set up. Fritz and I did a show several years ago with my Atma-Sphere amps and his speakers. We also had a 300B SET amp and it was surprisingly a great match for the speaker. Fritz's speakers are typically 6 ohm and a pretty flat 6 at that, with very benign phase angle. They are not high efficiency either. Duke LeJuene has praised them as the closest thing to a free lunch and I often point out to people they are the best kept secret in audio.

While I think @atmasphere made some very good points about distortion and speaker efficiency (pay attention to his example of the 4 ohm efficiency calculation using 2.83V), there is something to be said for designs that are not high efficiency. In my collection, my best speakers are not the high efficiency Audio Note AN-e or my DIY single driver using an Audio Nirvana driver, they are my Spendor 1/2e, Quad ESL, Acoustat Model 2, and Analysis Audio Omega. None of which should be confused with high efficiency.

Its always important to be careful about conflating personal anecdote with how things are: just because you have one efficient speaker that is bested by others of lessor efficiency does not mean that what I’m saying is incorrect.

@atmasphere I don't believe I was indicating your statements are incorrect. I actually said you made good points regarding distortion and speaker efficiency. My anecdote was strictly to illustrate my subjective preferences. In learning from one of the best engineers in the business who touted that greater benefits could be achieved from his amps if they were light loaded due to lowering distortion, making the amp work more efficiently, and extending tube life, that obviously aligns with your comments. From an engineering and design perspective, this is just the way it works, there is nothing otherworldly about it. That same engineer designed OTL amps. His preference would have been using them with 16 or even 32 ohm loads and he often lamented the lack of speakers being manufactured with those specs. As I told him and as I'll state now, unfortunately the audio world we live in isn't going to change course. We're not going to see a huge spike in the manufacturing of high impedance, high efficiency speakers anytime soon just because it's the better method.