Of course Topping is using a DC-DC stage for the output amp stage, converting 5v into +/-8v. Nobody is denying that, on the contrary. That was talked here several months ago. My suggestion was to use an external output stage altogether, straight from the DAC, which can still have linear DC if you use a linear power supply on the Topping. As the output from the DAC is balanced there shouldn't be much trouble. Then connect that to an external analog stage, with a fully regulated linear supply, higher voltage, like +/-15v.