I have made some experiments with USB sound devices on my Powerbook (A1138), since I received a LogiLink one at my workplace for Web meetings.

The result is:
- The device is recognized, appears in the Audio menu though most of the controlls are disabled. (Except Sample rate and Volume)
- I set it as the default device, but there is no sound by trying to play some music with Jukebox/Ambient's built in player.
- Trying with Aminet Radio (selected the card in the audio settings) made the miracle: The music was coming from this device. The volume could control only with Aminet Radio. The system volume control made nothing (even if this device was the default).

After failing with the USB device, I was fooling around further with the built-in audio on my Powerbook.
Tried to use an older pice of recording software, and also the new recorder tool.
Finally, only the new tool could make a recording in the case if one of the AppleI2S... AHI devices was selected. The internal microphone's signal was recorded. If the music playing was ongoing, the recorder couldn't allocate AHI device.
The other tool could do almost everything, but the created .wav file was not playable. Also monitoring wasn't worked.

Some questions arise while experimenting:
- What is Unit0 exactly, and What is the difference between Unit0 and AppleI2s... devices.
- What is the difference between ++, Hifi and normal devices.

Questions to the MOS devs:
- Two tools can open simultaneously AHI for playing (also works fine), but the recorder can't allocate AHI, if a music playing is ongoing. Is it a shortcoming of AHI?
- Do you plan to support the Powerbook's line-in?
- What are the biggest problems with AHI?
- IS it possible to record and play audio at the same time now?