A couple things to share:
1. Be wary of upgrading to OS X Mojave. The WM1x firmware installers don't work on it. Had to use a laptop with High Sierra on it to change the firmware.
2. For the discussion re: the SR15 vs WM1A, I had the pleasure of testing both out a week before buying. The SR15 has significantly worse sound quality and a far different sound sig to my ears than the WM1A, but is FAR FAR more responsive and practical in terms of portability and features. The sound sig out of the SR15 has a wide but flat soundstage (think IMAX theater), the upper mids and treble seem brighter than necessary (almost as if the tuning emphasizes these frequencies to make it sound on first blush that it's higher resolution than it truly is), the bass is tight but lacking. Was a fatiguing listen for me. Very HD800 in signature. The WM1A had a very wide, but deep and round soundstage, like sitting in the middle of a planetarium. The sound is significantly more detailed and fluid, especially the mids, and far more enjoyable to listen to and less fatiguing. However, as has been noted in this thread, the WM1x is not the most practical device, outside of its amazing battery life. FWIW I am using a 64 Audio A12t, not full sized cans (these pair extremely well with the WM1A, especially v3.0 of the firmware)