Well, as for our speakers, obviously we voice it with our amps....btw, we have a lot of manufacturer who are doing this using our amps with their speakers, from Magico down to independent small guys.
Anyway, there are 3 overriding factors for me, which I am preaching for 26 years now !!!!!
1. emotion 2. sound staging and huge predence and 3. tonality, lack of fatigue with precision neutrality
This all combined will give you your close your eyes, drift away and get you emotional orgasm, no matter what gear you have IF it is done right, i.e. musical and involving. Of course there are myriads of other factors, e.g. control, speed, dynamics, micro areas, etc. etc. But ultimately, and purposeful this simple, these 3 factors are 90 % + of what you would get hooked on.....
Now, as with the amps: they are by my own set-up just a tad to the warm side of neutral. Many reasons, call it vast synergy with existing speakers out there. However, there are severe cases where a speaker can sound either bright, analytical, or thin on one side, or others that are overly rich or bloated on the other side. That's where the bias comes in. All amps have to be biased, set up internally for best performance and reliability. However, very few of them can actually be used to tune your system. Sure, with tubes you can alter the sound quite a bit by tube rolling, but not necessarily within a given design.
With our amps, we can actually make the amp a little leaner, or detail oriented, or a little fuller, richer....just by changing the bias. I only base this on the tonality of speakers, not on specs. Don't care about specs, care only about ears....
Then there is a 3rd dimension in severe cases, which is the listening environment itself, but that's one of those )&^*%$&$($(&^$^(*_^_(^$% issues, but the actual results of what you hear can be adjusted somewhat by me with some biasing as well.
All of this has been learned over the years by countless installs, and feedbacks from some of the 4500 + customers of ours. I have a pretty good database of levels of synergy with speaker models, and what to do, but the single most important help is to get the info including voltage from our customers.......
Late,
Klaus