Yeah- those LUXMAN amps were pretty cool!
Blindjim, Here is how it seems to work: regardless of the amplifier, there are speakers it will work with and others that it will not. In the case of an 8 ohm speaker that has dips, the dips are of no consequence to a tube amp as long as its a crossover we're dealing with. What **is** of consequence is when the impedance maintains a sustained drop, for example when there are dual woofers in parallel (like in the B&W 802). There is no tube amp in the world that can play a B&W 802 properly (there are some that do OK) on account of that issue.
Here's why- if you use the 4 ohm tap, there will be ringing in the mids and highs because the output transformer is not loaded correctly. If you set for the 8 ohm tap, you won't be able to get enough power to the woofers- it will likely be a good 4-6 db down! The B&W was designed for an amplifier that can make constant voltage into any load (double is power when impedance is cut in half).
Conversely a transistor amp of 250 watts cannot make bass on an ESL (Sound Lab for example) because the impedance of the speaker is a lot higher in the bass than it is in the mids and highs. That transistor amp might be limited to no more than 30-60 watts into that load!
So matching is important, and yes, we do try to check and see what a potential customer is using on this account. Of course I like getting a sale, but it will do no-one any good if the amp won't work with the speaker, so I've had to steer sales away from us a number of times in the past on this account. After years of this, I realized that there was a bigger issue- that equipment matching, tubes vs transistors, objectivist vs subjectivist are all the same conversation- thus the link I dropped earlier.
Making power with tubes has always been expensive, and I have really come to value efficiency in a loudspeaker as long as it does not impair detail and bandwidth. That is a sometimes a tall order, but the speakers exist, but probably a topic for a different thread.