All of the retrocomputer designs need custom ARM firmware, because the firmware includes the ROM images from the specific machine (e.g. OS 1.20, Basic II and MMFS for the Beeb Model B). These are loaded into external SRAM just after the FPGA is configured.
So you will need to do an ARM firmware update to run these designs.
I'm not going to be much use here, because I'm not a Mac user.
You need to be connected to the more central USB port.
The dfu command I do on Linux is:
sudo dfu-util -d 0483:df11 -s 0x08000000 -D iceboot.raw --alt 0 -t 1024
The -d parameter is optional if you only have one DFU capable device connected.
But the other are important.
As is running as root (i.e. sudo).
So all I can suggest is you try to replicate this on the Mac.
Also, make sure you have the libusb package installed, as I think dfu-util uses this.