Document multi-API serving tradeoffs in TTS profile

Signed-off-by: Sy03 <1370724210@qq.com>

vllm_omni/deploy/qwen3_tts_high_concurrency.yaml

@@ -9,6 +9,15 @@
 # Profile validated for the c64 / PROMPTS=512 performance experiments:
 # Stage 0 talker on GPU 0 with S0=64, Stage 1 Code2Wav on GPU 1 with S1=10.
 #
+# For CPU-bound frontend or orchestration workloads, this profile can be used
+# with ``--api-server-count 2`` or higher to run multiple API frontends over
+# one shared set of local stage engines. This can improve request parsing,
+# multimodal/audio preprocessing, and response handling under concurrency;
+# it does not duplicate GPU engines or make a single GPU-bound request faster.
+# Each frontend keeps process-local state, so runtime voice mutations, sleep /
+# wakeup, async video jobs, and resumable duplex sessions are not supported
+# with more than one API worker. See docs/cli/serve.md for the full boundary.
+#
 async_chunk: true
 
 connectors: