While I’ll second Lorie’s concern about the quality of the speakers, I have to disagree with the observation that the amp has no aux-in/RCA.
The systems is 2.1, meaning two satellite speakers and one subwoofer. The 4th box is the amp/cd player/tuner/etx.
According to the LG website:
In/Outputs:
USB 2
Portable In Yes
AUX In (L/R) Yes (1)
Speaker Out System Jack
FM Radio Antenna Yes
So, yes to AUX In. And in the picture showing the back of all 4 units (like in the link in the OP), you can see the relevant RCA connectors to the right of the antennae connector.