Jult52, you hit upon my next area of interest, comparison to NOS DACs. To date I have heard some such as the Niko but not done side by side comparison. I know that users of NOS DACs are claiming wondrous things for them, so it should be intresting to compare.
However, I'll be honest; I have reservations that any 24 bit processing, NOS or not can perform at a level of that achieved by the stacked and paralleled ESS chips. I had an opportunity to use the PerfectWave transport/DAC which I believe has a "Native" setting and let's just say even the previous version of the EE DAC comapred quite favorably to it.
However, I am open to correction through comparison over time.
The SS output is a bit more pristine but a tad thinner, with less body, not dramatically so, but noticeably. The use of the stock tube vs. others might depend heavily on the rest of the system. But the extreme revelatory nature of the DAC is such that all tube rolling is highly efficacious.
If the rig is bass-shy I sometimes use the stock Shuguang over the Siemens, but with some loss of fine detail and air on the top. I have been staying with the tube output to add a bit more fullness in the bottom end; the Legacy Whisper DSW's in my rig are open baffle and are 22Hz, but I try to get as much out of their bottom end as I can.
I also cannot stress enough the importance of finding a superb digital cable. The quality will literally kill the performance or allow it to shine through beautifully. I would try no less than three different brands and perhaps as many as five or six to find one that is superlative - this is true with any DAC. If I were not reviewing and shooting for my best I might try as many as six to nine different digital cables; they make THAT much of a difference to the end result!