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

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.

I have a medium Wireworld which is fine but nothing special. I made the mistake of buying on Aliexpress (seller RYCFENZ HIFI Store, but the name may be temporary. Because they keep changing). Said the threads were of silver, &c. When the cable arrived, it didn't even work and the seller gave me a terrible service, lying in the dispute, saying that my device was not compatible, even though I sent photos and videos. Here is the alert for those who are still looking for an i2s HDMI cable.

The  New top Tubulus I2S X cable $1500

better then then anything I have heard to Date  and coming out with a matching flagship usb cable that will be just over $1k