This 2.1 PC amplifier is serving our kitchen with music using some in-ceiling speakers, and I thought it would be great to synchronize the kitchen audio with the audio played in the living room, over WiFI.

Supplies

Old (or new) stereo or other amplifier with a line in input

LinkPlay (Arylic) audio streaming board

Step-down DC-DC converter (5V out)

Some heat-shrink tubing, Ty-raps, wires

Step 1: Finding the DC Power

Locate the amplifier's power supply and follow the wires to the on-board DC power supply for the amplifier.

Carefully power up the amplifier and measure the DC voltage that is used to power the amplifier.

Step 2: Measure the DC Voltage and Connect the DC-DC Converter

In my case, this amp has a 16-0-16V power supply, but other amps may have other voltages. Some even have 5VDC power on board already, so in that case you will need to verify if you can draw 1A extra from this supply to power the Linkplay module.
Important: check if the ground that you use is the same ground as the line in ground.

Simulate the voltage you measured with a lab power supply and connect the DC-DC converter.

Adjust the output voltage to 5V.

Now un-power the amplifier and solder a red and black wire to the board where you measured the +16V and 0V.

Connect these wires to the DC-DC converter input, and double check the output to be 5VDC when you power up the amplifier.

Wrap the converter in a piece of heatshrink and glue it to an appropriate spot.

Step 3: Find a Spot to Mount the Linkplay Module and Connect the Audio Lines

Find a good spot to mount the module and connect the 5VDC wires to the board's screw terminals.

In my case, the amplifier has a separate line in board that I could solder a nice connector to, so that I could leave the supplied flatcable in one piece. But in any case, cutting the connector and soldering the wires directly to the board is fine as well. Alternatively, you can use the 3.5mm jack input of the board.

Connect the left and right channels. At this point, like I mentioned earlier, it is important to know if your amp power supply 0V is the same 0V as the Line in grounds. If it has a different level, you may blow your Linkplay module, so be careful and double check.

Step 4: Mount the Antenna and Roundup

Stick the WiFi antenna to the inside of the plastic housing. If you have a metal enclosure, you may want to consider mounting an external WiFi antenna.

The board also has Bluetooth capabilities, When you want to make use of this, you can connect a separate bluetooth antenna.

Step 5: Download the App

Download the 4STREAM Android or IOS app and power up the amp. Follow the instructions in the app and you are good to go!

I have a similar device in my living room which I use as a master device and multimple slaves that play the music that I select in the master.
Many of these systems are quite expensive, but with some handy hands and these inexpensive boards it is a lot of fun to stream your high quality audio throughout the whole house.