There are many synonyms for the phrase "more low-keyed", which means something that is quieter, less intense, or more restrained. Some potential synonyms include "muted", "subdued", "soft-spoken", "restrained", "modest", "understated", "relaxed", "calm", "gentle", "reserved", "subtle", "unobtrusive", "toned-down", "unassuming", "quiet", "peaceful", "serene", "tranquil", and "laid-back". Depending on the context, any one of these synonyms might be a better fit than another. For example, "muted" might be appropriate for describing a speaker's voice, while "reserved" might be better suited for describing someone's demeanor or behavior.