The SU9N is the high performance version. It has a switching power supply and does not have a femto clock. The D1SE has a linear power supply and dual femto clocks. The SU9N measures better than the D1SE across the board. The SU9N measures better in the power supply and jitter as well. The M500 MKII is the same as the SU9N but measures slightly even better and has a outstanding headphone amp. It is still no match for a $1,000 headamp though. What I would like to know is how is the topping D90SE better than the SMSL SU9N or M500 MKII, at $900 when the SMSL offerings are $440 respectively. The Topping is slightly better at THD+N but the SMSL's are much better at overall noise. In fact, those two SMSL have the lowest overall noise of any DAC's made to date. The SU9N and M500 MKII have custom clocks, not said to be femto. However they have lower jitter than the accusilicon femto parts. The switchmode power supply has lower noise than a linear power supply due to usage of the ESS power IC. To get better than these, I feel that you need to step up to the Gustard X26 Pro for $1,500. The SU9N and MK500 MKII are better DAC's than the D1SE to answer that question straightforward. Of course it ultimately boils down to what you like the sound of best of course. Also, as everyone knows the amp will have much more influence on the sound than the DAC. I personally would save money and get the outstanding SU9N or M500 MKII and spend the rest on a great amp that I like. Otherwise, get the X26 Pro. That is a huge step above any of these. Still, I wonder who would spend $900 on the D90SE. I feel that is a huge waste.