Glad to have finally joined the Utopia club after hearing them at CanJam NYC earlier this year! Now, to read up on aftermarket cables ... the obsession never stops ...

I can't speak to the technical details, but I went through a similar progression through inputs and ddc minus the spdif (amanero usb -> rj45 i2s -> hdmi i2s). To my ears, they biggest improvement was moving from usb to rj45, although there was definitely an improvement moving from rj45 to hdmi...

From Master 7 Thread:  

Has this been confirmed?  I am very interested in this for Singularity 7.

  A lot of people have been praising the results with the SU-1 vs. other options.  I kind of wish I had gotten an SU-1, but I ordered the AGD DI-U8 and noticed a clear improvement over the amanero using both RJ45  and HDMI I2S.  From the Master 7 thread, I read that Kingwa is working on a new...

I just swapped the RJ45 I2S for HDMI I2S and liking what I'm hearing.  Thank you for the cable recommendations, I went with a Wiredworld chroma 7 for now.  Immediately I notice an improvement to impact / dynamics.  There seem to be other improvements that aren't jumping out at me, need to do...

This is somewhat OT, but I am also about to replace the RJ45 I2S with the HDMI I2S module and was curious if anyone had a recommendation for a very short HDMI cable.

Jason, thanks for all of your contributions to the two Utopia threads.  Have you heard anything about a balanced cable in the future?

  Strange, I have been ordering from Massdrop for several years, and have never gotten any apparent marketing junk mail from audio or other MD communities.  That's not to say it couldn't be from them ...

  A lot of people really favor OTL tube amps with the HD650, many of which are single ended.  It might be that your dream setup will be single ended, and you won't even need a balanced cable.  Balanced doesn't equate to "better", although amps that are specifically designed to work balanced...

  What are you plugging the 6XXs into?  If you don't have a quality source/amp, the money you might spend on cables would be far better spent there.

Maybe I'll have to order a SU-1 as well to compare ... and so it begins.

  I bought the HD600s about five years ago on a ridiculous sale - I too have always wanted a pair of HD650s.  I immediately noticed how apparently worn my HD600 earpads must be, and also how much the clamping force must have loosened over the years.  The 6XX clamping force struck me initially...

I ended up ordering a DI-U8 since they are upgraded to the XU208 now and AGD is running the 5% New Year's discount.  Maybe I will get the chance to compare to a singxer SU-1 at a meet soon.  Has anyone compared the RJ45 I2S to the HDMI I2S specifically?  I ordered the replacement HDMI input...

I'll come to the next meet, just got a NOS11 and DI-U8 from Audio GD and my trusty NFB-10SE.  Have HD600 / HD650 / HE560 and , and I am eyeing getting another pair of headphones and a nice tube amp in the near future as well.