Ok, one ebay guy sent me his used grey velour HD560 pads, and I get that, why he says these are the best pads for HD540.
The argument for it goes like this: HD540 is a reference headphone, and therefore it suffers from being tuned to more bass and sharper sound with pleather pads, or blunted with unsuitable material as Memory foam is. These headphones show their timbre very much only with very soft wrap material as velour or fabric, that is filled with "non-memory foam" sparse foam. That is why old grey velour pads sound so good, because the foam is sparse (thin) in them. The timbre is exceptional with them. There is no comparison to it, forget wang's pleather pads, that make your HD540 sound too universal and bass heavy. They are the closest how pleather can get to timbre. I tried new Sennheiser replacement HD560 velour pads as well, and the magic is missing, because the foam is not sparse enough. You really need old foam, and then soft velour or fabric wrap to get to the magic. So how to get there without buying all HD560 headphones that are sold on ebay and get their old worn pads from them? Wel,, there is a solution to this
. Buy fabric option of these pads
https://www.ebay.com/itm/Upgrade-leather-Cushion-ear-pads-for-AKG-K701-K702-Q701-Q702-K601-k612-k712/322924921469?ssPageName=STRK:MEBIDX:IT&var=512043796368&_trksid=p2057872.m2749.l2649 . Then demolish it = tear the back plate off and remove and throw away the memory foam. Then get a soft sparse foam (not memory foam) from some cheap hifiman pads (or from used pleather pads), put it into the fabric wrap and glue it back close to its original shape with textil or shoe glue (I even glued the rings there) The resulting pad will not be as tall becaue such foam does not hold the shape as well as memory foam, but it will sound much better - less veiled, better then somehow bright and thin sounding original Sennheiser replacement HD560 velour pads, you will get 90% of sound of grey HD560 stock pads. Still, some sweetness of timbre and shape of space is missing, but it is a close call. There you go. No need to buy and resell HD560 headphones, unless you want full 100%.
I will further experiment with cotton wool filling instead of sparse foam.