Which HDMI for audio

Oh, if you want to keep the cable pure copper, you can try the Purist Audio Design.  Uses 24awg solid-core long grain copper conductors.  Very full and natural sound, but it is slightly warm and does not have the attack/immediacy of the silver-plated cables above.  It's relatively cheap at $215 (retail) for 6 feet.  Just depends on what kind of sound you want.

for comparison:

Nordost Heimdall 2 - 25awg solid-core silver plated 99.9999 OFC with micro-monofilament wrapping (provides more air around conductor and reduces dialectric absorption of the insulation).

Wire World 5-2 - 24awg solid-core silver-clad (heavy) OFC

Wire World Silver Starlight 6/7 -  2 x 26 awg solid-core silver-clad (heavy) OFC conductors per signal pin. This actually causes small errors in timing because the conductors are twisted and non-equal lengths.  That's why I do not recommend DNA Helix design for any digital cables.

Neotech NEHH-4200 - 26awg solid-core silver-plated OFC

Audioquest Vodka - 30awg solid-core silver-clad (heavy) PSC

Purist Audio Design - 24awg solid-core long grain copper  (better than OFC).  NO SILVER

@auxinput  That helps! Thanks. 

Are the Purist and the Neotech certified for ARC / eARC?

The Neotech page says it supports ethernet channel, but I don't know about the Purist.  You can email them.  They are very responsive.