I will try to suggest, as I too have the 1266, TC and Atrium, and I have a Susvara as well. They are all so different, in ways you will know, and the Susvara is different again. It is without a doubt an addition rather than crossing over into enemy territory in any way. If I had to pick, I would say that the TC is the closest, but even then they are plain different. The Susvara is the mature, wise one. Marry her to the right DAC and AMP and she can also kick some ass. I know this because when I first got her, she did not, she was too subdued, though brilliant in her subjugation. And now she is a menace when required. I cannot give you all sorts of technical details as I am not that kind of listener and do not possess that kind of knowledge, but the to the best of my ability the Susvara soundstage is not as wide as either 1266 or Atrium, but wide enough, instrument separation and imaging magnificent, but so are the 1266 and TC. Susvara bass won't quite thumb the way a 1266 does, I would say she is closer to the Atrium, that also has sublime bass. The biggest difference by far I would say is in the tonality and balance, where the Susvara is more grown up, and you would use her for different kinds of music; where the Abyss, whilst versatile enough to be good at almost everything, I would choose for Rock, and electronic and pop and just generally more in your face and upbeat music, the Susvara, whilst also being versatile enough to be good at almost everything, I would choose for Blues, and Jazz, and R&B, and classical, and country etc... Susvara you can also stick on your head and forget, whereas the 1266 doesn't let you rest in peace and dwell inside the music so effortlessly. In summary, the differences might be subjective to a large degree, but my word it will be different and if you are blessed enough to have all 4, you should allow yourself this experience, it is absolutely wonderful.