I spoke with Ayre earlier this week about using the AX-5 with headphones and iESL and the like, so I figured I would key in the forum.
Ayres official line is no HP boxes on the AX-5 and the reason for that is that some headphone adaptor boxes ground the negatives together which can cause issues. Using a direct speaker tap to 4-pin adaptor for headphones is totally fine and iESL will work as well. Other estat transformers should work as well but they didn’t look at internals to confirm (so long as its true balanced input and not dropping a pin/shorting to ground you are good to go).