This is probably basic but I just wanted to know what is the difference between S/PDIF, ADAT, and AES/EBU as far as connectivity.
S/PDIF, AES/EBU and TOSLink are electrically different, but the data they carry is potentially the same. They handle data in several incompatible formats. S/PDIF is unblanced coax, AES/EBU is balanced coax, and TOSlink is optical. The 0's and 1's can be the same or not, but the actual cables are incompatible. S/DIF and AES/EBU can often be made to interconnect and exchange data via special cables and/or transformers.
TOSLink and ADAT are physically very similar if not identical optical links, but the data formata are incompatible.