Couldn't stand the thin, flimsy cable that came with my HD600s which always ended up looking like a tangled mess on my headphone stand no matter how tidily I tried to store them. Read on another thread that the HD650 cable was much sturdier & had a 6.35mm jack so decided to order it. Was surprised to find it was less than £9 with free delivery & yes it is much sturdier & easier to store away neatly. A no brainer imo if you own HD600s unless you need the 3.2mm jack & don't like using an adaptor.
TS
I've just replaced the earpads on my HD580s but left the foam out as I thought it just cosmetic.
Does it affect the sound greatly, should I put it back in?
Yes, available here. Sennheiser tend to very good with spares, IIRC every single part for the upper range models like the HD-600 can be bought as a spare. You can still even by the yellow ear pads for the classic 1970s HD-414!
Proper ‘right to repair’ compatible kit!
No, the ear pad clamps it in place, so you'll have difficulty removing the old ones unless you remove the pads.Ah sorry I should have made myself clearer. I always knew I could get it. The question is can you actually fit it in isolation, ie without having to rip off the whole earpad?
I always like the idea but took the cheapskate route and have some of these for my Senns, AKGs, wireless AKGs and work earphones https://www.amazon.co.uk/dp/B071S5JH2R/?tag=pinkfishmedia-21Best upgrade I did for mine was to buy a rather nice oak stand from a seller called 'Oscar's Audio' on ebay.
I don't know what "diffraction side" means in OP. If it's the thin foam covering the drivers, just rip it out. It's the source of the infamous Sennheiser "Fog."