Direct monitoring is the obvious answer, but asking a question like this it would be good to offer the information
needed to get a more detailed picture of the issue.
What is your ASIO latency set to? Do you have FX enabled while recording (compressors or reverb)? Are there hungry-or-and-many VSTs running in the project outside the tracks you're recording? Are you using Scarlets own ASIO driver, not ASIO4ALL? Is the Scarlett the only soundcard selected anywhere in SONARs settings?
Your gear should easily handle the task, but you say lowering buffer/latency halts the machine. So, what kind of values for ASIO latency or buffer sizes you're using when the machine halts??