Glad to hear that it works well on ASIO. It confirms my guess that a problem is with PC configuration or a system is heavily loaded. ASIO is bypassing Windows sound setting, giving application more control over device, it is one things. I suggest to test bit-perfect Windows configuration, to see whether system-wide mixer is bypassed or not. A good test is playing DSD files. If you get a noise and a DAC/DDC is reporting DSD, it is not bit-perfect path. The other one (more complicated issue) is that current Amanero Windows drivers chose bulk transfer mode (like with hard drives). It works bit-perfect till USB hub is heavy loaded, as there is no bandwidth reservation that audio streaming modes acquire from the system. It is why I suggested uninstalling Amanero drivers for testing. Windows built-in UAC 2.0 drivers use asynchronous transfer mode that feature bandwidth reservation, possibly the same mode your DAC use when connected directly. If switching to the Windows drivers fixes the issue (like ASIO did), then with bulk transfers (Amanero WASAPI drivers ) you should chose a different USB port which is served by a different root hub.
I think you are wrong about ASIO. There is no conversion, no packet loss. The same with WASAPI exclusive mode. Both should deliver the same performance, but with WASAPI an additional configuration for exclusive mode is required in Windows Sound control panel.