Any old Cortex M7 with an i2s codec is plenty powerful. What sets the ADAU1701 apart is that it doesn't require any programming, you can't for instance make a FIR filter with it. You can give it a small set of FIR filter coefficients and it will do it, but you're not the one making the FIR filter program.
The Teensy I think has the biggest hobbyist community programming audio DSP not on PCs (lots of DSP plugin development for PCs obviously). There's also the Bela DSP, which can do thousands of taps of straight FIR filtering. Don't think anyone implemented zero latency FFT based filtering yet unfortunately, so if you want multisecond reverb or room correction you'll have to implement that yourself ... the ADAU obviously ain't going to do it either though.
Everything which is not ADAU requires more programming though.