I have to laugh. You say that like it's a bad thing. I am pretty sure everyone on this forum has their own set of preferences! If you think the YG is absent tonal liabilities then you believe in the fairy tale of the perfect speaker, in which case I can't help you understand. The flat-frequency-fetish design priority of the YG results in other sacrifices. Now, I have no issue with YG designing from a flat-first conviction. That's a legitimate starting point. But to sacrifice everything else to that, well that's going to stimulate some rebuttal. A polar graph of musically convincing attributes will not be a perfect circle. So let's be serious. YG has one way to build a speaker. Keith likes it. That's what matters in his decision. If the YG really just "lets the amp do its thing..." then I would have expected Luxman and ARC to prove more successful. Clearly, the YG doesn't just let the amp do its thing. It wasn't something very specific.
But, just where complex music guarantees a lot of collisions between upper midrange in vocals and convergence of guitars, strings, brass, percussion, etc., YG sticks a crossover point (1750 Hz), and this is where the speaker has its greatest trouble. The crossover creates a dynamic choke point that doesn't keep up with the rest of the frequency range. The speaker has trouble keeping simultaneous events untangled and you can hear the strain in the choke point. This also leans out some of the character of voices and instruments, especially voices above their fundamentals, compared to some other systems. From a frequency distribution standpoint the YG is a relatively objective speaker. But it will make a "cool" amp sound leaner and colder than it is, but will not make a "warm" amp sound as warm as it actually is. Is this a high fidelity crime? No. Nothing's perfect and the designer made some choices that lead to this. I can't help it if someone else doesn't hear it. But there it is. The speaker has great bass when coupled to an amp that can drive and control the low range. Bass quality is essentially beyond reproach for something you can put in your home. The top end sounds harmonically dry -- perhaps a trifle harmonically incomplete -- but that's a smaller point and easy to get around. In the midrange, the speaker can do solo singer + one or two instruments well. With the Ampzillas it can deliver more explosive dynamics than I expected (but not as explosive as I can get out of 25w with 101db/w/m speakers) and that seems fine in Keith's room. In a room half again larger, more power would have to be found.
It's the unfortunate crossover point choice (well, if you're going to have a crossover in the first place) combined with the design mandate for low efficiency which sharply restricts amplification options, that most limit the YG. On crossovers, bingo -- my preferences not only do not include crossovers -- since Zu, Audience and a few others made crossoverless speakers practical and musically convincing -- I am adamantly opposed to crossovers, and the longer I am absent them in my systems (crossoverless since 2004) the more obviously I hear crossover liabilities undermine music. I paid my crossover dues and hacked my way out of that dystopian jungle for 35 years before making it to a clearing. But I have no specific bias for or against aluminum in boxes. Aluminum can be structurally effective and properly damped, if the designer pays enough attention to those factors. Aluminum in drivers? Well, no, not my first choice, but again, if you are a speaker designer and choose to use aluminum drivers, then prove to me you can use it properly. Just understand that today even paper can be an advanced material.
The YG isn't, as I wrote before, my kind of speaker. But if a friend buys them, then I'm interested in getting the system with them in it to sound as convincing as possible for the choices made. As a 3way, YG did a much better-than-usual job of making a crossover-intensive, multi-way loudspeaker sound reasonably coherent. The drivers have nearly uniform dynamic behaviors. None of the drivers sound less disciplined or substantially differently-behaved than the others. His claimed very good phase coherence sounds largely born out in listening.
In a lot of ways, a "cool" speaker is easier to live with and compensate for than an overly warm one. The YGs won't give Sinatra a head cold. But they can give him a Vegas-arid scratchy throat or some strain from desiccated vocal chords even when it's raining. The speaker gets tangles in full orchestra crescendo for similar reasons. These may be minor points to some people. Some people don't hear it. Some people hear it and don't care. Some people hear it and will never buy that speaker. People do what they do. Until someone asks me for a recommendation or opinion, I don't care what they buy. But when they ask, neither a dealer nor anyone else can expect me to defer. What I hear, I will say.
Phil