There are differences between 222’s pre-amp and Atom HE’s pre-amp.
- Atom uses op-amps (compact small-signal audio ‘operational amplifier’ chips), 222 uses discrete transistors
- Atom uses a chip based volume control, 222 uses a resistor ladder and reed relays
- However they both have the same headphone amp circuit. With small changes to some parts.
The sum means the 222 is better as a headphone amp than Atom HE. It is significantly more expensive and doesn’t not have the array of headphone sockets.