Well, they're in! (Oh, my cable assembler was Mike B, not Matt). So, my MA3s had the 10 day burn in, so ~240 hours, but they did sit unused from shipping, on Monday, until last night, so that could be a factor. I immediately heard differences between the MA3 and the Monster Reference cables that they replaced (about 15 years ago I worked at a retailer whose only decent cable was Monster, and employees got 60% off retail, so most of legacy cables are Monster).
Overall, the sound was smoother, particularly in the lower treble on up. With the Monster, there were some upper-mid/lower-treble areas that would kind of jump out at me (not in a good way). These jump-out frequencies were gone, replaced by some lesser jump-out frequencies lower down in the mid-band. They were noticeable, but not nearly as bothersome. One big area of improvement I heard was in the decay of cymbols, which seemed to go on forever. There was a smoothness to the sound that might be what TAS's Jonathan Valin (and HP before him) call "continuousness". Soundstage seemed a little wider, and there seemed to be more depth as well. There was an increase in detail, with certain lines of music becominng much more easy to follow than with the Monster. Bass seemed to have a little more definition, with no big difference in output, although there seemed to be an increase in the "subterranean" feel of really deep synth bass (Soundtrack to "The Mission", by Vangelis, track 1).
One thing that I noticed was more frequent spine-tingling running up the back of my neck, and my desire to keep listening past bedtime. Another point in favor of the Morrow is that a ragged zone of treble, like in the 5kHz range, which I had accredited to my speakers (Ohm Walsh 2000) vanished. So, happily, it seems this was not an issue with the speakers. And no, this did not occur at the expense of any treble detail or extension.
Music I listened to included Veruca Salt ("25"), Angelfish ("You Can Love Her"), Count Basie ("Kate" from 88 Basie St. XRCD), the Vangelis soundtrack for "The Mission" and others. All from my server, all 16/44 resolution via my Squeezebox Touch to my Superberry DAC (a highly modded Beresford 96/24 DAC), to my McIntosh C220 to Odyssey Audio HT3 amp to the Ohm speakers and Vandersteen 2Wq subwoofers.
Now, I realize there is still much break-in to occur, so that is why I am not going to call this post a formal review. But I am impressed. I would like the mid-band to smooth out a bit more, and hope they will. But even at this point, they are a clear improvement over the Monster Reference.