I am looking for a high-quality HDMI cable for I2S from a CD Transport to the DAC...

I could not advise you on that since I have never used i2s myself.  From what people say, i2s is superior over S/PDIF.  However, some things to think about:

i2s - this requires a very short cable (1-2 feet).  The interface does not work well with longer cables.  Also, the largest awg conductors you will see are about 24awg in the largest HDMI cables.

AES/EBU - you can run this very long (15-20 feet is no problem).  It also opens you up to a larger selection of cables and also cables that have much larger conductors (like 18 or 19 awg).  In my experience, this gives you the best bass and depth of sound.

Uhm, if you use the HDMI cable for actual HDMI audio/video source, then 2 meter is definitely better.

However, if you are using this for i2s, then you still want the cable as short as possible (like 0.5 meter).  The i2s interface is different and was not designed for long cable runs.  I'm not sure how well the Heimdall will work out for you.  Hopefully, it will be an improvement.

For AUS/EBU cable, Tara cables look good, but they definitely get expensive.  I would ask them what size conductor they run.

I just recently had a discussion with another forum member.  He ended up getting an Acoustic Zen Absolute 110 cable.  This uses a large 19awg solid-core pure silver conductor.  It's close to my own custom built cable.  It is one I would recommend at this point.

Get aTubulus Concentus i2s Cable. It is a dedicated cable just for audio. It won't work for your TV, I had the top of the line Wireworld Silver HDMI and the Tubulus is much better. More open, better tonality, more dynamic, etc. Really a big step up.