Nice to hear from people who've worked in this field.
I am unsure to fully understand what exactly is your project, however with audio processing, you usually have to sample an input signal (44.1 KHz ?), output an analog signal and in between process some digital filtering. You CAN do all this with an arduino DUE.
The Due only has 12-bit ADC's and DAC's - I wouldn't reckon that good enough for serious quality.
The Due is fast - but it's not a dsp. These are specifically optimised for filter work with fast floating or fixed point multiply and accumulate (MAC) instructions, barrel accumulators etc. TI, Analog Devices, ON-SEMI etc all do good ones. Their design is quite different from general purpose processors such as arduinos.
They are also fairly expensive and use a lot of power, and their programming is not trivial. DSP programming is a specialist highly mathematical field - learn about Z-transforms if you want to make a start.
As mentioned above, many people have addressed guitar signal processing problems over the years, and there are many commercial products available.
Doing better than these offerings if new to the field is unlikely to be easy. Though skilled in audio electronics, I wouldn't even try.
Allan