I sympathize with both the seller and the buyer, assuming that they were not defective when sold. With proper freight shipping, they should have arrived with no damage at all, either to the speakers or the boxes. The fact they there was visible damage might indicate that something happened to them while the pallet was being loaded or transferred, perhaps.
That being said, Seller very reasonably offered to have the speakers repaired under warranty. How would he have known that it would take 6+ months to get the replacements? Similarly, Buyer acted very reasonably in accepting that offer, rather than returning the speakers, which he was certainly entitled to do, since he bargained for receipt of working speakers, not blown ones.
So what now? Clearly neither party contemplated that it would take so long to get the replacement. Buyer is completely justified in requesting a full refund. It is seller’s responsibility to get Buyer a working pair of speakers and he didn’t, whether his fault or not. That is why I ship anything expensive with insurance. Seller is clearly obligated to refund the money and take the speakers back.
I can easily relate to this because I shipped a DAC to a Buyer, and the screen (finicky on this DAC) worked when I had it in my system and didn’t work on arrival. Luckily, the screen wasn’t necessary to get it running since it has an app, but I gave Buyer the option: return it for a full refund or I will pay to get it fixed. He chose to hold onto it and get it fixed. Manufacturer has had the screens on backorder for 2 months now, and I told Buyer that and again offered to take the unit back. My reputation is far more important to me on here. Buyer again confirmed that he didn’t care, and may not even repair the screen, although I told him that would be a mistake, since he would have to fix it at some point. Bottom line is that sometimes crap happens, and it is neither party’s fault. The Seller is ultimately responsible for getting working equipment to the Buyer. Period. Seller has to suck it up.