I did a frequency response test (using miniDSP EARS & REW) on my SMSL SU-8 v2 DAC and found that the phase performance is strange. I used 2 headphones: Sennheiser HD650 & Hifiman HE-4XX, both single-ended. I also compared the SU8 to 2 other DACs: Grace SDACB & XiangSheng DA-05B. All DACs were paired with the Monolith THX AAA 887 balanced headphone amp. In all the tests (SPL, distortion, GD, Clarity, etc.) except for phase, results were similar. However, for both heaphones, the SU8 phase was -90 & -128 degrees. For the other 2 DACs, the phase was 81 & 53 and 80 & 52 degrees. My question is, is the -90 & -128 degrees phase for the SU8 something to worry about?