Well I just grabbed a used pair of HD-6XX off r/AVexchange. They sound awesome through my SMSL iDEA dongle DAC, but I’m not very impressed with their build quality. My Final Sonorous III’s are waaaay better. Are 650s built better than the 6XX? I guess I was just expecting more.
In any case it doesn’t matter that much to me since the sound good. I expect they’ll sound even better when my Schiit Midgard and Modius arrive in the next couple day.
I’d say the 6XX is the best built 600 model out right now. The 6XX uses the old plastic mold, which is the same one that lasts decades. There’s still old 600s and 650s from the old mold that have lasted all this time, and have a reputation for their durability.
The current 600 and 650 models have a new mold which is more angular, but also uses thinner plastics. Going from my 6XX to a modern 600 felt like the 600 was way cheaper built and lighter (although I’m sure it’s still durable)