I am looking for a USB audio interface that I can connect all of my instruments to, and I have been considering a Focusrite Scarlett 18i20. I have an electric guitar, an electric mandolin, a Hammond SK1 organ and a Roland Gaia synth, and I would like to connect them all to the interface simultaneously, which shouldn't be a problem as there are enough inputs for this. However, in the interface manual it says that instruments can only be plugged into inputs 1 and 2 directly. If I wanted to connect all of the above instruments, can I do that directly or will I need some DI boxes? If so, how many would I need? The Hammond requires two inputs (L+R stereo) and the Roland requires another two (L+R stereo again). Would each line require its own DI box?