DS1 is the second device select, leave the jumper where it is.
Some manufacturers number thier drives 0, 1, 2, & (sometimes) 3, while others use 1, 2, 3, & 4. How the device is selected also varies from one make to another. IBM & most clones chose to set all drives as the second device, and re-arrange (twist) the cable to line it up with the correct pins on one of the drives. Before IBM-PC, I don't think anyone else used this method. I'm looking at a Texas Peripheral drive right now, and all four DS lines are connected, with no jumper block present. The intention was that the user/installer would cut the three unwanted traces on thr PCB, leaving only one device selected. However, when Tandy used these drives in the TRS-80s (the one I have was pulled from a Model III), they chose instead to use the data cable to select the drive, by not populating the connector with the unnecessary pins. Other makers used still different methods. Your Amstrad, f'rinstance, uses DS0 & DS1, as the drive maker intended, if I understand you correctly. Note that there will not be a twist in that cable.
--T