So I am able to give some impressions of running the 560s from speaker taps. Sadly, as I changed both amp and cable I am unable to say anything about how the Norne cable may or may not have affected the sound, but I will say this, the cable is stunningly lovely in an understated way, and so very well made. Anyway, that was an aside for the moment.
The 560s are now very holographic sounding to me, even more than I remember (audio memory not being perfect of course). There is so much more weight to the lower frequencies, and the mids have really come alive. For certain the NAD M3 is voiced slightly warm, which I feel is a great signature when well done and smearing avoided. Personally I think it is far easier to remain faithful to the recording intent erring on the warm side as opposed to the neutral side, but that is another story.
I already played my music about as loud as could be done without being painful so I am very sure despite not doing any SPL measuring that I am not listening with the NAD at a louder volume. If I was, that could explain some of what I am perceiving, but not all, and in fact, I find once playback gets louder, the weight of the music gets thinner. Exact opposite has happened here, everything has far more weight to it, with the exception of the slight "de-emphasis" on the upper frequencies (which I actually think is great with the well extended 560).
This seems like a contradiction, but despite the lessened treble (really slight attenuation by the NAD, but noticeable even with my speakers) I am hearing quite a bit more detail. Suddenly drums are revealing much more of the sound they would be laying out in the studio during the recording. There is a more natural acoustic timbre to the drums and with electric guitars I swear I am hearing a far more natural sound. There is quite a bit more low and mid bass, quite a bit. Not D7000 level of bass, but as you would expect with the 560, more articulate presentation in these frequencies.
Vocals are also seemingly more forward than they were with the A18, going by memory of course, but I would wager this will bare itself out even when I have my now sold A18 back here for a listen. As I think I mentioned before, I am lucky enough to have sold my A18 to a very experienced head-fi member who lives here in Ottawa, so a direct comparison will be possible in the very near future.
I feel very relieved as what was a big leap of faith has really exceeded my expectations thus far. Now it wasn't inexpensive to do so, the cable cost me more than I sold my amp for, but I have no regrets at all. I will take a few pictures soon I promise. Anyway, if any of you are on the fence about trying a speaker tap with the 560, taking amplifier synergy into consideration, and all things being equal I enthusiastically say give it a whirl. I can't imagine how much more I might have had to spend on a high end head amp to get this level of sound quality. Who knows, maybe I wouldn't have to spend much more than the A18 costs me, I can't be sure, but my instincts tell me that I would have to dig pretty deep into my wallet. It does appear that the beefier and more stable the power supply, the better the signal reaching the transducer will be. Just opinion of course, and mostly speculative opinion at that so certainly take it with a grain of salt.