I was afraid it would be too good the be true :(

You're quite right that the linearity needs to be good and at high gain,
however I'd be inclined to use a passive 20dB per step attenuator on the front
to maintain a good overload margin.

Ah.  Indeed, 384 kHz output is now not expensive at all (probably the sound system for my next BNR build, though I'll use 96 kHz of it max), but 384 kHz input is still usually about US$1500 and up.  I did find one for US$600:

https://www.amazon.com/Singxer-Digital-Interface-Femtosecond-Interfaces/dp/B07M72XCZX/ref=sr_1_fkmr0_4?ie=UTF8&qid=1547205969&sr=8-4-fkmr0&keywords=384khz+record