That's good to hear that it's not Sabre based. The PCM179x is not my favorite, I still prefer Analog Devices or Asahi Kasei Microdevices, but it's a decent DAC, much like the Wolfson WM8741. The amount of hype surrounding ESS and the Sabre has just gotten completely out of hand. According to several engineers, it's also by far the most difficult S-D chip to work with to date, with a spec sheet that's full of holes and misinformation.
The problem with the 1704 is mostly one of cost. If you're building a reference level DAC you really need at least eight of them, four per channel. With current prices you're talking $550+, just in DAC chips. Contrast that with the sigma delta chips which all run about $10 ea. Somebody needs to come up with a new R2R chip for the modern age. Aside from the 1704, the only other one really left standing is the Philips TDA1543, which was never very good.
MSB does offer their R2R modules as OEM, but from what I understand the cost on those things is quite dear.