Interesting, just 5 minutes ago I came back from the Mytek shop (which is a few blocks away from my studio) and I had read your post before I went there and decided to ask there for you...
The owner and designer of all the gear showed me one of the Mytek A/D D/A converter and swears that it sounds better than Pro Tools HD converters. Of course he has an interest in saying that but he also says that listening to HD is like listening to something through curtains and listening to the same thing on Mytek is like opening those curtains.
I personally never used the Mytek converters (I have other Mytek gear, which is why I was there) so I didn't get a chance to A/B although he was kind enough to offer me to borrow his converters to try them out...
He did however mention something that might interest you.
He said that if you go here (let me get the link for you):
MYTEK DIGITAL USA
you can actually listen to samples of different A/D converters.
He pointed out that it is not a true test because you are still listening to your Pro Tools D/A converters (the true test would be to listen through Mytek D/A converters) but at least it is a place to start...
You probably already knew about that link, but the other interesting thing I can tell you is that he told me he has more tests that he is going to upload... I tried to get him to do it right away for you but he was too busy and it might probably take some time for him to do it, but maybe you can keep checking back on the website...
I hope that helps a little bit