There's also
Neutrik NMJ6HC-S, which is the same jack as stock (non locking, switching function), but with chrome ferrule.
(https://forum.bottlehead.com/proxy.php?request=http%3A%2F%2Fwww.neutrik.com%2Fwebsite%2Fuploads%2Fimages%2F06%2F660x%2Fnmj6hc-s.jpg%3Fv%3D2&hash=51a7b4e917b7d78d947ec2229d7edee98042cadc)
Not an upgrade, just a different (potentially nicer looking) jack. I didn't want locking function on a small headphone amp, so I opted for this one.
It's funny how you can find RCA jacks worth tens and hundreds of dollars, but there's almost no boutique headphone jacks... How are we to make the complete signal path with the same type of connectors, as some advise, if I can't get my solid silver headphone jacks, plated with finest hand picked mountain rhodium?