I still have my old Koss 2+2 Quad Headphones, and they must be 31-32 years old. They still play like new, look like new, and also sounded very good, similar to a Koss Pro4A, but I agree, one certainly won't get the full true effect of quad like sitting in a room surrounded by speakers.
These have the bladder rubber Earpads similar to Koss Pro4A Phones, so no deterioration (yet) They have individual Volume Controls, and a 2/4 Channel Switch.
Downsides (like the Koss Pro4A) they are heavy, not exactly the type of headphone you'd want to wear for a great length of time in a warm room, and after a long period of wearing them your head feels like it was in a Vise. Mark