I set the headphone output up on your specific order based on the headphone information that you provided. So your headphone output is not the stock output. But your overwhelming complaint about the bass is dully noted. I sent you technical information on how to reverse the changes to your specific order. If that doesn't help, by all means send the DAC back for a refund
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But in general, this type of complaint does highlight the reason why I am preparing for the sale of a new kind of headphone amp design. No two customers have the same opinion of what a headphone output should sound like. Being able to adjust it to taste will be a great advantage.