Any headphones
Crossfeed works in the signal, so it works with wired headphones, a DAC, or Bluetooth. It is not tied to a brand or a head-tracking feature.
The presets
Default (strongest), Chu Moy (middle), Jan Meier (gentlest), from the bs2b library. Chu Moy is a good start. How bs2b crossfeed works.
Where to find it
Settings → Sound → Crossfeed, under 8D. It is free on every platform.
Frequently asked questions
Is crossfeed the same as Apple’s spatial audio?
No. Spatial audio renders surround mixes around you, with head tracking on some headphones. Crossfeed gently mixes the two stereo channels the way speakers do in a room.