I am going to add to this just for the sake of getting it out there in case someone else is attempting this.
Using my little G4 MacMini, I can compile a native version of tetheredboot and/or injectpois0n, then using the commands shown on the internet I can run tetheredboot or injectpois0n -t and it starts to work, but then this happens:
Device must be in DFU mode to continue
opening device 05ac:1227...
Found device in DFU mode
Checking if device is compatible with this jailbreak
Checking the device type
Identified device as AppleTV2,1
Preparing to upload limera1n exploit
Resetting device counters
Sending chunk headers
libusb:error [darwin_transfer_status] transfer error: device not responding (value = 0xe00002ed)
this error repeats 11 times total then we get:
libusb:error [submit_control_transfer] control request failed: no connection to an IOService
this error repeats 42 times, then we get:
Sending exploit payload
libusb:error [submit_control_transfer] control request failed: no connection to an IOService
Sending fake data
libusb:error [submit_control_transfer] control request failed: no connection to an IOService
libusb:error [submit_control_transfer] control request failed: no connection to an IOService
libusb:error [darwin_reset_device] ResetDevice: no connection to an IOService
libusb:error [submit_control_transfer] control request failed: no connection to an IOService
this error repeats 4 times, then we get:
libusb:error [darwin_reset_device] ResetDevice: no connection to an IOService
Exploit sent
Reconnecting to device
libusb:error [darwin_close] USBDeviceClose: no connection to an IOService
Waiting 2 seconds for the device to pop up...
Connection failed. Waiting 1 sec before retry.
this error repeats 10 times then we get:
Command completed successfully
Unable to reconnect
Unable to upload exploit data
DFU Exploit injection failed (4294967295)
Exiting libpois0n
-------------------------------------------
So, this seems to indicate to me that the issue lies either with with libusb directly or with libusb.dylib and Apple's own HID driver grabbing the device exclusively. Now, I have no clue how to fix this, and I am probably totally incorrect anyway. Anyone that is smarter than me have any insight as this seems to be the only issue making it so that people cannot use an older PPC Mac (10.5 anyway) like a G4 Mac Mini :) to do the tethered boot.
I don't mind waiting too awful much for an untethered jb for this thing, but it would be cool to not have to restore the thing every 20 minutes while I am trying to get something to work :)