They could have used Amazon Custom (which is a new service that's mostly focused on apparel, but still) or Amazon Handmade (Amazon's Etsy clone) instead of using the typical system for selling manufactured products. They were setting themselves up for failure by selling an artisan product on a marketplace designed for factory produced goods.
It makes no sense to criticize Amazon for being what it is, which is mostly a platform to buy standardized, affordable, manufactured stuff.
They went into the Amazon Vendor program not really understanding what it entailed. A lot of big companies that also participate in the Vendor program have similar complaints about it to this guy (especially in regards to price inflexibility) but there are similar problems when you sell to any big retailer. There are also plenty of problems and headaches with, say, selling to Best Buy or Wal-Mart, that you don't have when you sell to Amazon.
They could have also just focused on eBay and taken advantage of the more lenient return policies. Or just focused on their own website. I understand why all of this would be confusing and frustrating if they are primarily a small niche manufacturer accustomed to selling direct to high-end consumers on their own website.
But that would have just been successful for them and not have made a good viral marketing blog post that hooks into a ready mass of resentful people who are looking for something to be mad on the internet about.
TBH they would make more money by figuring out how to reach audiophiles who want high end custom speakers on Amazon than just trying to gin up outrage with a coupon attached to it. Some people would rather be mad than just quietly successful. The overlap between people who get outraged against big corporations on the internet and people who want to buy $335 desktop speakers is very limited. Better off finding those rich and picky audiophiles and appealing directly to them.