To be honest, I've no idea what "cast to device" means. If it means you want to initiate the playing of a file from your W10 computer to the 1800T, then as far as I can see there is no way to do this. As BH pointed out in post #4 the 1800T has a DLNA server which can serve StdDef files to other devices. It has to be turned on. "Read the fine manual". It is also possible to use the 1800T as a DLNA client. If you can work out how to set up your W10 computer as a DLNA server, then you should be able - from the 1800T - to view a file stored on the W10 computer.
I only make use of the video folder on the 2000T (essentially the same as an 1800T). You can transfer pictures/music/video to the Humax via ftp. I've never tried to upload music or photos via a USB device so I don't know if that works. As BH says you can play video/music and view photos directly from a USB device.
I have never seen any reference to the 1800T/2000T being able to use SMB.