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?