Sorry, I remember you saying that. I have never experienced that amp/dac but have only read good things. My suggestion woukd be to stick with them for a week or so. Play all types of music through them and use good recordings. You will then be in a better pslosition to evaluate thr purchase. I have always prepared myself for dissapointment when buying new headphones ever since I was underwhelmed with the venerable HD-650s, which I have learned to love over many headphones I have tried subsequent to my adaptation to them.
It may still be you are disappointed, but it is worth it to give them at least a few days' chance. I absolutely love my HE-500s for what they do.