Spot on. There are differences, but not such that one is definitively better than the other since there are variables relating to the phones, DAC and the source as well as the tube used in AIC which all come into play. With the right tube, source and DAC, the AIC is a perfect match with 1266 Phi TC imo and, in my setup, I actually slightly prefer the XLR headphone out with 1266. We cannot really speak in absolute terms about things where there are variables involved. As ever, it is a case of YMMV. Trust your own ears is always the best advice. Nothing else matters.
One more thing for folks to consider is this - what I described means that like each of these outputs has a slightly different output impedance, so damping factor will vary and this will impact different headphones differently, and different chains, differently.