Ok, so I was prepared to give Amiga Explorer a go... I followed the instructions and all, but when I typed "Type SER: to RAM:Setup" on the amiga (to transfer the Aexplorer software from the PC to the Amiga) I got the "Error, bad args!" message in CLI.
I think it is because I didn't use a workbench disk, instead I used a disk that has a workbench-interface and a CLI-prompt.. (the disk contains a virus killer program). But I'm not sure this is the reason for the error. What else could have gone wrong (except cabling)?