Don't forget the negative cash flow that the manufacturer has to withstand as the program is started up.
For example, a pair of speakers that retails for $6000 might be rented for $100 per month (for "full payout" in 5 years). It might have cost the manufacturer $3000 to make the speakers, but he won't recover this initial cash layout for 30 months. At the end of year one, he will have spent $3000 but collected only $1200, so he's out of pocket by $1800 even after collecting 12 payments.
Now, multiply this by perhaps hundreds of pairs of speakers that he might lease in the first year of a leasing program, and it becomes clear that most high end speaker manufacturers can't do leasing. I believe most high end manufacturers are not known to be particularly highly capitalized, and the cash flow burden of having to purchase materials weeks and months before making a sale is by itself already a stretch, let alone supporting a lease program.
Of course, they could always make a deal with a bank that would do the leasing program, kind of like an auto dealer that introduces you to a local bank for a car loan or lease. Maybe this would be more appropriately performed by the high end hifi dealer instead of the manufacturer. At that point, you might as well just get a personal loan or lease from a bank all by yourself, which you could do now.