I found a way to sync local audio output.
1. install tuneaero
2. in tuneaero preference menu --> multi-zone -> add reciever -> specific audio device, choose your local speaker audio device from
the pull-down menu, and give it a name ( for example, "Local PC Speaker" ) then save it.
3. with tuneaero in background, run tuneblade, you will see "Local PC Speak" in the list of AirPlay device.
4. in tuneblade preference menu --> audio capture --> set capture mode to "virtual device loopback",
you need to install VB-Cable ( it's free ) first, then you can choose line-in device and output device to VB-virtual cable ).
5. now play PC music, your local PC speaker will play, but it use default win10 driver,
then when you active "Local PC Speaker" from the tuneblade airplay device, it will
a. mute win10 default pc speaker driver so there will be no sound at first.
b. then it will capture audio from VB-virtual cable device
c. and it will send the captured data to airplay device "Local PC Speaker" ( from 2. you named it at tuneaero preference )
6. tuneaero will sync all the "airplay device" including "Local PC Speaker", so your local PC speaker will sync with other
real airplay device such as homepod...etc.