wget http://bues.ch/b43/fwcutter/b43-fwcutter-018.tar.bz2
wget http://www.lwfinger.com/b43-firmware/broadcom-wl-5.100.138.tar.bz2
tar xjf b43-fwcutter-018.tar.bz2
cd b43-fwcutter-018
make
sudo make install
cd ..
tar xjf broadcom-wl-5.100.138.tar.bz2
sudo b43-fwcutter -w /lib/firmware broadcom-wl-5.100.138/linux/wl_apsta.o

a reboot or modprobe b43 should get the device driver loaded, and wifi available.  I also had to set the wireless interface to "wlan0" in wicd preferences., but this might be done automatically if you reboot rather than use the modprobe command.

This machine doesn't look like the one pictured on your link, snork.  The EFI situation could be similar though, I don't really know.  It does seem to be from the same era, though.  This is an all-in-one thing (basically the hardware is all mounted behind/under the screen.  no tower, more difficult to replace individual parts).

inxi reports this as:

System:    Host: imac Kernel: 4.19.0-14-amd64 x86_64 bits: 64 compiler: gcc v: 8.3.0 Desktop: Xfce 4.12.4 tk: Gtk 2.24.32 
           info: xfce4-panel wm: xfwm4 dm: SLiM 1.3.6 Distro: Devuan GNU/Linux 3 (beowulf)
Machine:   Type: Desktop System: Apple product: iMac6,1 v: 1.0 serial: <> Chassis: type: 13 v: Mac-F4218FC8 
           serial: <> 
           Mobo: Apple model: Mac-F4218FC8 v: DVT serial: <> UEFI: Apple v: IM61.88Z.0093.B07.0706281250 
           date: 06/28/07 
CPU:       Topology: Dual Core model: Intel Core2 T7400 bits: 64 type: MCP arch: Core Merom rev: 6 L2 cache: 4096 KiB 
           flags: lm nx pae sse sse2 sse3 ssse3 vmx bogomips: 8645 
           Speed: 1589 MHz min/max: 1000/2167 MHz Core speeds (MHz): 1: 1101 2: 1049

Unfortunately, I am not able to boot the amd64 debian buster netinstall cd, either.  The prompt that comes up trying to boot any amd64 disc (so far) is:
1.
2.
Select CD-ROM Boot Type :
(and all keyboard input is ignored at this point)

Also, thanks for the hint on using the desktop *live* installer disc.  I'll try that next, I think I should be able to get that to work.  Even if I can't boot it directly, I should be able to mount it and run the installer from it.

The live isos use refractainstaller. Here's a pictorial guide if you are not familiar with it: https://www.devuan.org/os/documentation … f/live-gui

1. Use "dd if=/path/buster.iso of=/dev/sdX bs=4M" on existing machine to write the Debian Buster net-installer to a USB stick
2. Complete the install with only "standard system utilities" selected (deselect Debian desktop & print server)
3. Migrate to Devuan with a slightly modified version of this

# mv /etc/apt/sources.list /etc/apt/sources.buster
# nano /etc/apt/sources.list

# apt-get update --allow-insecure-repositories
# apt-get install devuan-keyring --allow-unauthenticated
# apt-get update
# apt-get upgrade
# apt-get install eudev
# apt-get -f install
# reboot

# apt-get dist-upgrade
# apt-get purge systemd libnss-systemd
# apt-get autoremove --purge
# apt-get autoclean
# nano /etc/network/interfaces

# reboot

Then install whatever desktop environment you wish [if you wish].  If you are installing on an encrypted partition and are getting "blah blah busy..." during your reboots you should install cryptsetup-modified-functions and if your video just gives you a blinking cursor instead of your X login manager you may need to add non-free to your sources.list and install firmware-linux-nonfree.

PS: I happened to use my "mishka" mirror but you could of course just use deb.devuan.org if you don't want to.

Does that get you any closer to the goal?