Hi Lea,
SAM does support inverters with up to four inputs, but for now it can only model a system with one multiple-input inverter. You can connect more than one subarray to the same inverter input, so you could have a system with three subarrays with a two-input inverter, for example.
SAM can only model a system with one type of inverter, and one type of module.
Best regards,
Paul.