Pulseaudio – How can multiplexing multiple channels into one?

I’m trying to multiplex (mux) the multiple sinks into one sink. like below

[sink #1 / 2ch] - (left)   ---- (front left)  - [sink #3 / 4ch]  
                └ (right)  ---- (front right) ┘  
[sink #2 / 2ch] - (left)   ---- (rear left)   ┘  
                └ (right)  ---- (rear right)  ┘  

As I know, there is module-remap-sink, but I think that is for demultiplexing.
So, is there any way to realize above mux?

I can realize that just using module-loopback. like below

pactl load-module module-null-sink sink_name=playback1 channels=2 channel_map=front-left,front-right sink_properties=device.description=playback1
pactl load-module module-null-sink sink_name=playback2 channels=2 channel_map=rear-left,rear-right sink_properties=device.description=playback2

pactl load-module module-loopback latency_msec=30 channels=2 channel_map=front-left,front-right source=playback1.monitor remix=no sink=FOUR_CH_SINK
pactl load-module module-loopback latency_msec=30 channels=2 channel_map=rear-left,rear-right source=playback2.monitor remix=no sink=FOUR_CH_SINK