I'd just use an outboard dac and use the Behringer only in the digital domain. That's exactly what I do. I can't imagine what mods would do to make the digital domain any better and an outboard dac leaves alot of choices. Therefore use the money for a better dac. That's my opinion anyway.
I actually use an older Bel Canto DAC 1.1. This thing is good enough for me and is excellent. Thought about getting a newer dac but this thing for 450 bucks is keeping me happy. Getting the latest and greatest of 4-5 years ago in dacs is a good option as you can get them at a fraction of the price of new dacs and performance is still excellent.
I actually use an older Bel Canto DAC 1.1. This thing is good enough for me and is excellent. Thought about getting a newer dac but this thing for 450 bucks is keeping me happy. Getting the latest and greatest of 4-5 years ago in dacs is a good option as you can get them at a fraction of the price of new dacs and performance is still excellent.