Hydrophone ADC with Programmable Gain

I’m developing an embedded system for underwater acoustic measurements and I need the complete signal-conditioning path designed around a high-resolution ADC. The hydrophones capture low-frequency signals and will sit at the end of a short cable, so the front-end has to supply phantom power for their internal pre-amplifier, clean up the line, and digitise the result with selectable gains that I can command from my firmware.

Here is what I’m after:
• A low-noise analogue front-end that provides filtering, amplification and noise-reduction tuned for the sub-kHz band typical of these sensors.
• Software-defined gain control (digital potentiometer, PGA or similar) that I can drive over I²C/SPI from my MCU.
• Integrated phantom-power rail (12–48 V) with proper isolation so the analogue ground stays quiet.
• ADC selection and interface logic ready for direct connection to a Cortex-M microcontroller (I²S or SPI preferred).
• Schematic, PCB layout and BOM in KiCad or Altium, plus brief firmware snippets showing register settings and gain switching.
• Confirmation that the final chain meets a target SNR better than 90 dB over the 10 Hz–5 kHz band when tested with a dummy hydrophone load.

If you already have experience with low-frequency acoustics, delta-sigma converters, or have shipped designs that live in salty, noisy environments, your insight will be valuable here. I’ll handle enclosure and final firmware; I just need a clean, review-ready hardware design and the essential control code so I can drop it straight into my project.