Topping D70s is one of the best DAC's. The chip, AK4497eq, is maybe the most underrated from entire audio market. It has a very good performances, it sound is excellent, it is easy to implement. It don't need of I/V converter. Topping D70s need a fresh chassis, case, with a new screen. Maybe a new XMOS, XU316 and a powerfull output stage with OPA1656 op amp for example. Maybe a much powerfull power supply for all stages, with much powerfull voltage regulators, with low resistance PCB routes for power supply, etc...