New library for PWM playback from SD cards: SimpleSDAudio

I'd like to see/learn more about making this Awesome library better sounding with the use of filter/amp?

Small? (all SMD?)

Is there a schematic posted for it?

I am VERY happy Tuttut released this lib.. it was a HUGE missing part of the Arduino community (easy audio)..
but as 'stock' the volume is just 'meh'... so it needs some filters and an amp for sure for more sound hungry projects..

still learning/finding my way through filters and amps..

thanks!