Choosing SRAM for PIC project
Why use PIC24+sram when the newish PIC32MZ DA series have 32MB of internal/stacked DDR? TI has some nice adc codecs that mesh well with i2s. While I understand trying to keep it under one roof, I think it is better to add an audio adc rather than sram. Typical micro adc's aren't really geared toward audio anyway.

I'd guess that by the time you find 4mb of sram you'll about be at the cost of the DA series, especially if you figure the extra pcb layout time and layer count.

The current errata does limit ddr to 0-70C, but 32MB is real nice, it opens up lots of possibilities.