brundleflyPreferences > Audio > Playback and Recording > Always Stream Audio Through FX. This setting and functionality are new to X3. X1/X2 will behave similarly after you start and stop playback once, enabling the audio engine. But the idle load will still be lower because it doesn't stream silent audio through all FX all the time. The advantages of doing this are documented in the New Features section of the Ref. Guide.