Why 105? Because the dCS doesn't play multi channel SACDs, nor DVDA nor Blurays.
The 103 is primarily designed as a digital transport so the DACs used in the design (and the analog subsystem) aren't great to start with.
It does have the HDMI inputs so it can upscale lower quality video sources to 4k using it's good 4k video subsystem. That IMHO makes sense if you have a good 4K chipset and a 4K display (which I expect is the only reason you'd upgrade from a 93 to 103.
Adding async USB to the 103 is a superfluous component that adds to the cost of materials but isn't particularly useful for what it is used for.
The 103 is primarily designed as a digital transport so the DACs used in the design (and the analog subsystem) aren't great to start with.
It does have the HDMI inputs so it can upscale lower quality video sources to 4k using it's good 4k video subsystem. That IMHO makes sense if you have a good 4K chipset and a 4K display (which I expect is the only reason you'd upgrade from a 93 to 103.
Adding async USB to the 103 is a superfluous component that adds to the cost of materials but isn't particularly useful for what it is used for.