About the digital vs analog xfeed ...
.... well, I may be more enticed by digital xfeed if manipulates the signal temporally, only. That is, the analog xfeed seems to change the freq response based on what the other ear is expected to receive frequency-wise.
Well, it matters how it is done, but what is done. Unless Crossfeed implements the correct transfer function, it is immaterial if it is done analogue or digital.
But this means use of parts like caps and R's or even opa's to create a frequency filter. Like this:
First, this is of course "wrong Crossfeed". It first needs to be corrected to have the right transfer function.
Those parts add noise. A digital delay might be cleaner because of less parts and no frequency manipulation. It cuts right to the chase.
Yes????????????
Second, as shown (and as I always implement it) it actually forms part of a reference design headphone amplifier with LM4562 and LME49600 buffer and as such, there are no extra stages, no extra noise, distortion etc.
Plus a simple 2-pole switch into a virtual ground is all that is needed for disable/enable Crossfeed, making this very suited to the use of electronic switches in "zero distortion" mode.
To do it digitally with the correct transfer function may require a reduction in digital path gain to avoid overload.
Both analogue and digital approaches have respectively benefits and drawbacks. Either option can be great IF the correct transfer functions are applied and the drawbacks are minimised and the benefits are maximised.
To wit, if we make a fully digital system with a 5.6MHz digital amplifier driving the headphone, obviously a digital Crossfeed is the only sensible option. Adding a DAC, analogue Crossfeed and ADC to get Crossfeed would be madness.
If we make a completely analogue headphone amplifier, obviously analogue Crossfeed is the only sensible option. Adding ADC, DSP Crossfeed and DAC to get Crossfeed would be madness.
In-between, the choice is up to the designer.
Thor