I agree that there is some tech that sounds great for years, take for instance the Krell (legend, never heard) headphone amp or the older Headroom max amps (heard this one, beautiful sounding), both sound phenomenal to this day. That being said , there are significant advancements to DACs being made, I switched over to the Benchmark DAC2 and could not believe how much of an improvement in clarity and detail I hear over the Benchmak DAC 1, Rega and or the Bifrost Uber.
What did you make of this topic? http://www.head-fi.org/t/689783/december-2013-mid-level-dac-comparison/
I definitely agree the Benchmark DAC 2 would be an upgrade over all the DACs you listed, but in the last 3 years a lot of progress has been made overall, especially with USB implementations. The linked topic does throw an interesting perspective on current DACs available.