PulseAudio System-Wide Equalizer
Pi Core Player is an option too, It has an equalizer based on Alsa but it does not use the DSP in the the cirrus logic audio card, as far as I know.
PCP can be built to be a standalone solution, but it is not designed to operate like that. It is a minimalistic linux with a network audio renderer.
How ever it can be pimped to also host your Logitec media server ,have local storage and serve a portable wifi AP.
With some batteries you could use it as a walkman you can control from your smart phone.
Currently I have a similar setup built in an old portable radio, using the speaker-out of the cirrus logic audio card.
I want to use my Pi3 as a portable mp3 player. Is there a way to implement a traditional style tone control ? Bass, treble, volume ? If it has to be done in DSP how would I go about it, or should it be done in hardware? Always wanted to get into DSP apart from the textbooks, this seems like a good place to start. Perhaps the Wolfson Audio card would do the job? Thanks in advance.