I'm possibly more sensitive to the changes in sound that aftermarket cushions have on headphones. They definitely change the sound and often for the worse. A few years ago someone did an exhaustive test of how various aftermarket cushions affected the sound of a popular headphone. i think it was the HD650 or HD600. He used some sort of dummy head with microphones rigged up inside and plotted the sound recorded on a frequency graph. The aftermarket cushions measured poorly compared to the OEMs.
My personal experience with the pricier aftermarket cushions for HD650 is that they made the sound anemic and hollowed out because of the added cushion depth and stiffness of the foam.
The OEM pads for the Z7 can be purchased from Japan retailers for half the price that Sony's American parts store has them listed for. But you have to use a shipping proxy service. I was able to buy the OEM cushions so cheaply that I flipped a couple sets for profit on ebay. I keep one backup set in the closet ready to go when my current pads start to form permanent creases on the sides of the cushions.
These japan relatailer,do you have any source ? dont forget also consider for shipping and import fee, in my country now in Indonesia, shipping from china is free, i dont know how they do it, but they can, even that's took long to arrive, unfortunately for the rest of the world including japan, there's no such thing as free shipping and after some calculation it's definitely not cheaper, i found one on ebay, but sadly the item worth almost 2 times of the price of third party earpads and that's not including shipping cost and import fee as well which also almost 60% of the item price, it will be triple cost (not worhted it), no wonder no spareparts here available for now, also the not come up with the ring, if only sony sell those too, also most retailer in japan will ship in USA or europe but not want to ship to south east asia, even they can, the shipping cost almost the same as the item price itself
However if the OEM more cheaper, perhaps i will consider but as i realized the third party ones i had is not bad quality compare to the OEM or i can said better in comfort, let alone sound quality, probably also better in durability
There's funny story though, there's friend of mine buying this Z7 unit, the seller didnot tell the original earpads has been replaced by third party, and he thought the third party ones is original OEM parts since it's more thicker, also he include the OEM but it's already in bad condition, so the Third party ones attached by default
He was surprised that time when i told him that the thicker one is the third party pads instead
I talked about this earpads, this kindda have good quality compare the other third party ones (see the attachment), no wonder he thought this particular parts is the original, but the reallity, it's not, this is the best third party that i can find so far since i hardly find the OEM ones
Now maybe you can share how can i buy the OEM parts that comes cheap perhaps thats maybe same price as this one or even cheaper, and i wonder if they ship internationally as well because i couldnot find it yet