I have heard the HD 600 (but it’s been awhile). The HD 580 was Axel Grell’s first headphone design for Sennheiser. However, having talked to Axel, he says the plastic herringbone pattern grilles actually had resonance, and he felt he could bring the tuning closer to the original electrostat HE90 Orpheus (as close as a dynamic driver could, anyway), thus the Sennheiser anniversary edition HD 580 Jubilee (the Carbon Fiber appliqué one) which eventually became the production HD 600.Have you heard the HD600? Same thing. Literally the same driver. I ordered some custom grilles but I got an email letting me know they would be delayed a bit and haven't heard back.
That said, I’ve been reading impressions for months where people are just really digging the timbre and richness of the old original HD 580.