I'm sure you would know if your DH has had a DNA fragmentation test as it is quite expensive...maybe $400 or so!
I didn't try DHEA. I've heard of others trying it in my age group with mixed results. I was taking melatonin, coq10, vitamin d and fish oil for egg quality. But for me it didn't really help as age was not on my side. I would definitely try it if I were you though. It's important to take the right dosage of each and you'll need a script for the melatonin.
I wish you all the best. I think that you have some time to investigate what might be causing you issues and if using a donor is what happens then that option is always waiting for you if you need it.