PulseAudio – simultaneous output – add two devices

I am watching this example of how to add simultaneous mode support to PulseAudio. The example shows how to add just one device which is the hardware’s one:

### Load analog device
load-module module-alsa-sink device=hw:0,0
load-module module-combine-sink sink_name=combined
set-default-sink combined

My question is how to add two (or more) devices and how to add virtual devices?

EDIT:

I tried the instruction to combine two sinks:

$pacmd load-module module-combine-sink sink_name=combined2 sink_properties=device.description="Combined with a null sink" slaves=combined,MyTestSink

but I get the error Module load failed. Something’s wrong with the syntax or what else can be wrong here? I have the combined and MyTestSink names on in the output of $pacmd list-sinks.