Come collegarli è scritto nel readme di github della libreria
One or more MAX6675s can be bussed together to interface multiple
thermocouples. This library makes it easy to instantiate as many thermocouple
objects as you need. Connect all the MAX6675 Serial Out (SO) pins together, and
connect them to Arduino pin 12 (MISO). Connect all the MAX6675 Serial Clock
(SCK) pins together, and connect them to Arduino pin 13.
The Chip Select (CS) pin from each MAX6675 must go to its own Arduino pin; any pin can be used.
il CS ti serve per attivare di volta in volta il MAX6675 da cui leggere il valore della termocoppia