I wonder why LCD-X and LCD-XC immediately got put into summit fi subforum cuz they don't meet your 2nd criteria. I can't think of a reason yet beside the price tags. I hope to listen to them at the next meet.
Price AND probably branding..audeze and stax is standard considered summit fi by our moderators as far i can see it.. Whether u agree with it or not.. I get a feeling its all personal taste and pricing what moderators decide to put them in summit fi or not.
I myself know the he500 when being driven by the right amp can be a real killer phone.. I loved that phone..
For me..the he500 is high end.. It was once..when its pricetag was 899euro... It was so good people were choosing the he500 above the he6.., and its rumored that the price reduction of the he500 was only to protect the he6 sales back then...but its never proven... But it did make the moderators act to kick it out of summit fi...could that be the reason? As the phone didnt get worse..