Mmmm, maybe it's time I retrieved my old pair from the storeroom where they have been sitting for 2 or more years and re-acquaint myself with them.
They are indeed an interesting headphone which is why I kept them. As I...
In every EL34 based amp I have owned my favourite tubes have been NOS Gold Lion KT77s (if the amp can take them) and Mullard XF2s; whether or not they will play nicely with the CS600 I don't know but it is worth looking into.
The Afzelia will go a bit darker in time and the gold flecks will stand out more. I did not do my best job on rubbing out the finish so I will probably take it off again in a few months and start from scratch.