The DIY challenges:
- Poor value proposal versus many pre-built speakers
- Can't know how they'll sound
- Hard to know if you've built them right due to not knowing how they should sound
- Possible screw ups
- Proud papa syndrome (hard to be objective on how they sound)
- Count on resale value to be poor
From my experience, I find the value proposition of my NX-Oticas as tremendous compared to every pre-built speaker I've owned (probably 20 or so over the years ranging from $1K to $20K/pair), many of which were very highly rated by well known reviewers. By far the best performance/$, and in fact the best performance (with the subs) of any speaker I've owned. I've had quite a few people over to listen to them that concur with my perceptions.
While it may be less convenient or practical to hear them first, it is often possible if their is someone in your area that has built them or something similar. I have demo'ed my to a half dozen people since I completed them a few months ago.
Building the flat-packs is quite easy - no more difficult than putting together an Ikea product, for example. If flat-packs are not available, it's obviously more work. You could have a local cabinet shop cut the boards for you and do the rest of the construction and finishing yourself.
Building the cross-overs is a bit more complex, but there are plenty of people on AudioCircle that can help with guidance and feedback. It is possible to screw up, but it's more likely the screw-ups will be with finish quality, not sound quality.
I don't think "Proud papa syndrome" is relevant, even if it exists. If you like the way they sound, that's all that really counts.
Your last point is probably the biggest issue, but if you do a respectable job building them, it probably won't be hard to find someone that will buy them for your out of pocket expenses (or close) to avoid the time to build them. But you are right that you will never get a reasonable price for your time.
That said, I'm waiting for Danny's next masterpiece (Line Forces) to be available, and will jump at the chance to build them given the experience I have had with the NX-Oticas and subs.