Need advice and info about i2s DAC


Here my current setup : An Atoll in80SE amplifier / 2 JBL TLX16 SPEAKER / A Cambridge MagicDac 100 / RPI4 2 GO with volumio.

I’m new in the universe of DIY audio system, and recently discover that i could have a top-notch system for a good price.
So i want to make my system upgrade to something more DIY, with better components and quality sounds than today.
But i don’t really understand the world of I2S, HAT, USB signature, Digione…

Where can i learn a bit more about DIY system ? Maybe with explanations about which role have each cards ?
Which cards are needed to replace my current DAC ?

As example : I recently discover the sparky bundle (kali reclocker, allo piano 2.1, galvanic isolator…) The bundle seems to be appreciate by many pple. But:

Does the kali reclocker, allo galvanic isolator, the piano 2.1 44/48 are compatbile with my RPI4 ?
Will i gain in sound quality compare to my cambridge current DAC ?
Is it necessary to add the volt amp if the piano card is connected to my Atoll amplifier ?
Is it necessary to add the Capacitance Multiplier if i don’t use the volt amp ?

Thanks you for your answers and clarifications