Recording on iPhone from stereo line-in I'm looking for a way to perform relatively high quality stereo line-in recording on iPhone. Unusual and third-party hardware is acceptable, but jailbreak is not. I am aware of the following options:

Griffin iMic paired with Apple's Lightning to USB Camera Adapter


Pros: Well-reviewed, USB interface.
Cons: Lightning to USB Camera Adapter is not supported on iPhone.


Blue Mikey Digital


Pros: Works with iPhone.
Cons: Requires Lightning adapter, line-in quality reportedly poor.


Neither of those satisfies my requirements. Is there some workaround I'm missing?
Check out some of the electric-guitar-interfaces.  For example, the Line 6 Sonic Port Channel Audio Interface has a stereo 1/8" input jack available. On the pricier side though.