If it is possible to go into the M50 with a USB source (USB HDD, USB Flash Drive, or SD card) and output to a USB DAC, the M50 would replace a PC/Mac in the music file path, with a device that, hopefully, has its design specification based on sound audio principles. There may be other ways to achieve the same objective, but most alternatives seem to be particularly expensive.If you use the M50 with input (other source device) via Bluetooth or USB, then the M50 no longer acts as a player (source device) but only as a bridge. There are no more player functions, therefore no EQ functionality. In this mode, the M50 is just an interface converter.
What would be the point of going into the M50 with a USB source device and then connecting a USB DAC to the M50?
According to Topping's description, you can connect a USB storage device and a USB DAC to the M50 (player mode including EQ function) at the same time and play the music files from the USB storage device on the DAC.
The USB connections on a PC/Mac are notoriously noisy, particularly the power rails, since the power supply in a PC/Mac is unlikely to be optimised for stability. For example, there is a possible problem of a voltage difference between the 0V rail on a PC/Mac and the 0V rail on a USB DAC, or the CPU demand causing a dip in the 5V rail. These mght not be major problems but are a potential source of noise at the input to the USB DAC.
The table for input/output in the user manual for the M50 states: USB Storage Devices/HDD/TF card IN [can output to] Bluetooth; USB-OTG OUT; SPDIF/IIS OUT. Great, connect to the USB DAC using the USB-OTG connector as output.
The connection diagram for the USB Storage Device/HDD/TF card indicates a USB HDD or USB Flash Drive as input to the USB-OTG connector with the output taken from HDMI/OPT/COAX USB cable. Without the M50 available "on the desk" to investigate the menu settings to configure the input/output options, the manual seems to lack clarity when it is necessary to state how this combination of input/output is configured.
The user manual also shows file formats APE, WAV, FLAC and mp3 are "CUE supported". Hopefully this means that CUE files can be used to control playback, rather than having to select each track as part of a playlist. There is no further explanation of what "CUE supported" means.
Lastly the user manual states the HiByMusic app can be used as a control point. As the M50 is DLNA certified it should be possible to use any app that complies with the DLNA standard, such as Bubble, shouldn't it?
To summarise, all of these points suggest that there is a need to improve clarity in user manuals and not leave any aspect of the operation of a device to interpretation. Otherwise the M50 does all I want it to do, but it would be fantastic if Topping provided Amir with a production sample to see how the M50 stands up to rigorous testing.