I said maybe because I have not heard the 901 at all. I am trusting KKCC on this.
I think the Tera pairs best with the SE5 then with the 1plus2 and the AK120 pairs best with the 1plus2 then with the SE5. The Tera has a more musical, organic, analog sound. With the 1Plus2 Tera and AK120 are quite close, but I think the AK120 (on 1.00 fw) is slightly better than Tera. I would not say it is worth getting the AK120 for the SQ. Because it is different and you might not find it better. In any case it is not much better.