Would you rent a $14,000 DAC for $75 per day?

No. And it might have been $14K to the initial purchaser, but rental value would be calculated on used fair market value since a used article is what is rented. And then there is the issue whether any DAC is worth $14K given the considerably lower price points of other well-rated DACs.

Camera rentals are usually done by pros who need a specific piece of gear for a short-term project. Lots of professional equipment is rented this way.

A DAC at $14K (ridiculous, IMO) is rented to someone who wants to hear a particular piece of gear in their personal system who can then decide whether the juice is worth the squeeze. If the purpose is to then buy the DAC or not at new or used price, cost for the experiment $350+ shipping. That business model might work for some things in some places, but I doubt the extremely rarefied market of very high end gear would be one of them. Maybe if you were a dealer of that $14K DAC and you offered the rental service in a large metropolitan area to potential customers to draw interest, you might get a couple of takers, but the clientele would be a small and rarefied group. I doubt there are a lot of fence-sitters thinking of spending that much on a DAC who would be drawn by a short-term rental option, enough to make setting up the business worthwhile, even with the potential for generating a stock of used units that could be sold at a discount.

"But folks, you can rent virtually anything - cars, dump trailers, DJ equipment, $50k RED cinema cameras, boats, Ferraris, someone’s personal house, etc. Seems like the only thing you can’t rent is hifi gear. "

Not really the same. If I am a landscaper and need a Vermeer stump grinder or a forestry cutter, someone will rent me one and it is up to me to rationalize that cost to the project. Same with a RED camera. Both are rented as tools for a project. Renting a DAC for a trial is more like renting an article of clothing, except even then not the same. Clothing rentals are usually for a unique event and are done because the renter does not foresee an ongoing use case for the item rented.  I could see the service as an entree to purchase by a dealer (credit the rental charge to the purchase, if done.) A DAC is a permanent part of a system; you need one or you don't. If you aren't going to sell the same high-dollar DAC, why bother? I doubt there is that much curoisity to make a useful market. Of course, if you are looking to buy a stock of equipment  as part of a venture on paper, have a writeoff for the gear and occasionally rent the items, then that is a different issue. I can't see it making any real money, though.