I don't think 16-bit stereo audio at 44.1 ksps is possible. But I have been thinking about it for a while.
I can write a 512 byte block to SD in about 900 microseconds using a special multi-block write command. So about 1/3 of the CPU is needed for SD write at 176.4 KB/sec.
I am going to do an experiment reading out two ADC in parallel using bit-bang. I will connect a single pin to clock on both ADCs but have separate pins for data out. For ADCs that need input I would use a common data in pin.
My guess is that it will take too long.