Well, I was hoping that there would be something familiar among your list of recordings, Eweedhome, but, alas, I have none of these. Nor have I ever had the good fortune to hear the legendary Linn CD 12, but its reputation would have me thinking that that the culprit futzing with your string tones has to be something quite simple. Given that the 3As have a reputation for showing low impedance in the bass frequencies, I'd gather that the 4 Ohm setting on the ARC would produce the better sound.
If there are any similarities between our systems, they would be in our choices of amp and preamp. I run a 23 year old Quicksilver that makes 95 watts per channel, and a highly modified tube preamp that's based on the Marantz 7 design. This pair develops considerable dynamic range and good sound, but can sound a bit strident with many audiophile "sacred cow" accessories. I solved the string tone issue years ago by doing several things, including rolling literally scores of tubes through my components, then finally finding the solution by replacing the vaunted Telefunken 12AX7s with some Sylvania 5751s and replacing my speaker cables with those offered by Monarchy Audio. These might work for you as they are extremely smooth but open in the highest frequencies.
If there are any similarities between our systems, they would be in our choices of amp and preamp. I run a 23 year old Quicksilver that makes 95 watts per channel, and a highly modified tube preamp that's based on the Marantz 7 design. This pair develops considerable dynamic range and good sound, but can sound a bit strident with many audiophile "sacred cow" accessories. I solved the string tone issue years ago by doing several things, including rolling literally scores of tubes through my components, then finally finding the solution by replacing the vaunted Telefunken 12AX7s with some Sylvania 5751s and replacing my speaker cables with those offered by Monarchy Audio. These might work for you as they are extremely smooth but open in the highest frequencies.