Yes, the PCM270# series is a bit old and dates back to 2009, and before. However, I still think that for basic listening, they still perform well. They are a proven product. While the newer ESS Sabre flavors do offer the possibility of an improvement in areas, it still comes with a cost. I think when one factors in cost / performance, the Muse DAC for $30 is quite a good performer and for most people, spending upwards of $200, or greater on a better DAC, their ears might not be able to tell the difference when using compressed music as most people tend to do nowadays. Plus, we all know that the "better" options do provide some improvements, but usually those improvements tend to be a bit more costly and the gain to be only single-digit percentage increases. To me, I've tried far too many upgrades to realize that many were never upgrades at all, and each of them took a bite out of my wallet at the same time.
As to the DAC with the PCM2704c vs. the PCM2707, I still think the "04" option may still be fine and the "07" option marginally better. But, I have not heard both, so don't quote me on that.