Thank you for clarifying, I did notice that balanced XLR cable to my headphones has slightly less volume at the same settings on the amp and DAC, which the specs from the SMSL engineer confirm. Maybe I am just overthinking all of this. I just wish I wouldn't have dumped the money into getting balanced cables for headphones, DAC, amp, etc if they really don't make any difference... The price of all these XLR cables adds up fast. After the price match, the SMSL Su8 was 170 dollars so I know the value is good. I just wonder if I wouldn't have bothered with an XLR balanced DAC how much money I could have saved on the DAC and the cables, seems like a couple of hundred bucks, and if I am understanding what you are saying is correct, that couple hundred dollars registers inaudible quality increases from connecting to the THXSMSL 2000 through RCA channel.
Yea, things do add up quickly. It just depends what you are trying to achieve and what your priorities are, as to the value for you. For me I wanted:
1. A DAC that falls into the upper tier of performance measurables.
2. XLR interconnects to eliminate any chance of running into ground loops.
3. Maximum flexibility for future proofing, I hate buying something and then finding I need to replace it because it cannot do this or that. For example, a full range of input / output options. Right now I use a USB input from my PC (Geshelli DAC lacks this), an RCA connection from my STX Essence (Grace Design Standard DAC Balanced lacks this), and XLR interconnects to the amp (D50S, etc. lack this)
4. A DAC with a remote for volume control (since many amps have a degree of imbalance with the volume control), and to a lesser degree other features, Bluetooth being unimportant to me.
5. A DAC that is reasonably priced.
The SU-8 ticked all the boxes for me.
As far as balanced headphone cables, I did not expect inherent quality gains (some folk claim improvements, other say not), but with an amp like mine, I could tap into significantly more power via XLR, so being able to use the full potential I was paying for when needed.
I have no regrets or buyer's remorse, you got a good deal on your SU-8, I hope you will be happy with yours too!