Easy button is to use a MoTeC E888 expander, connect your type-K thermocouples to that, connect it to the M400 via the CAN bus, and configure the EGT inputs to use that.
Otherwise, if you have 4 available analog inputs, you them with an external thermocouple amplifier. I have been happy with products from Exhaust Gas Technologies, like this 4-channel amplifier w/sensors (but they sell parts separately):
https://exhaustgas.com/ProductDetail.as ... &BasketID=Lastly, there are some other brand lower-cost EGT-to-CAN devices, but you will have to setup their CAN output correctly, and by the time you do that, the E888 is the easier / more supportable option -- it is a lot easier if you have a MoTeC dash where we can more easily handle any CAN input, and then send it on to the M400 (plus log it!).