99 and 44/100% of any loudsepaker is the driver and very, very few manufacturers of dynamic loudspeakers build or even specify drivers; some big Chinese company produces a huge range of variations and they pick one. If you turn to the Japanese companies (TAD, GOTO, ALE) I highly doubt (but don't know for a fact) that they wouldn't consider any outside input beyond "thank you for the honor of allowing me to purchase your products".

So you're left with a company buying drivers and building a box to hold them. How hard is that really? The guy who designed and built the driver had an ideal enclosure in mind when he started. Ask him. If you don't want to ask him as T-S - they know to a very high degree of certainty.

And the crossover? I'm convinced that all the "mystique" about crossovers is largely manufactured - that even a textbook crossover will work just fine with well-behaved quality drivers. It's undoubtedly a challenge to knock off the peaks and dips in the response of some "Made in China" POS but that wasn't your point. And even if you engineer a brilliant response shaping network, how meaningful is it when applied to a line of drivers with poor quality control and large sample-to-sample variations?

As far as cost goes, look at the prices of Westlakes or Wilsons or those of similar stature - a speaker with perhaps $5K of drivers and materials at retail sells for $30,000 - there's a hell of a lot of $ for the DIYer to play with.

And what I think most important is that the DIYer doesn't need an anechoic chamber - he's building a custom speaker for a custom space, his livingroom - all that really matters is the in-room response he gets, not how his speakers measure in some absolute sense.

And another point - people who build and sell "statement" speakers with passive crossovers are just full of shit - there's no justification for a $30K pair of speakers with a passive crossover these days, especially as cheap as DSP has become. But again, it's part of the manufactured mistique - you use passive crossovers and your customer is much more likely to waste thousands on the speaker wires and amp-trading that your retailer relies on between big speaker sales.

And yet ANOTHER point - most loudspeakers above a certain quality level are a distinction without a difference, a matter of personal taste and peference (what the hell is a $50,000 Stereophile Class A loudspeaker with LIMITED FREQUENCY EXTENSION anyway???)

Much if not most of the consumer loudspeaker market is an exercise in illusion and intimidation - mass hysteria or a sort, assuming you're vulnerable to it.