This QC issue doesn't surprise me - first pair of HE-6's I received had no sound from the left earcup/driver, totally DOA.  
The dealer made apology and asked if I wanted a new pair shipped or refund - I took the refund.  
Chanced buying the HE-6 again after building up the courage and thankfully they were without issue, but pretty disappointing first time around and unexpected for top tier cans for sure.  
All I can say is that I'm glad to have taken a second bite at the HE-6's as they are just unbelievably good.  
The HIFIMAN HE-560's appear to be mimicking the wood style of the AUDEZE LCD-2/3's, whilst the AUDEZE LCD-X's appear to be mimicking the HIFIMAN HE-6's aluminium enclosures so perhaps each respective manufacturer is trying to take a bit of each other's market in the aesthetics dept?  
I've read contrasting reviews for the HE-560, some saying they prefer them over the HE-6 and vice versa, so it's naturally individually subjective, but I do like the wood styling and reports of improved comfort and lighter weight all seem positive.