I did it too
I think you can get those kind of wires with a 1/4'' big end (da san xin) and a VCR end (xiao xan xin). The sigal is mone so you need two wires for both L and R channels. Then you get the stereo sound. But the 1/4'' connecters with these wires are mono connectors, the sound quality may be reduced a little bit compared with stereo 1/4'' connecter (recommended by Echo MIA). But without prefessional monitors, this is the only choice.
Also. sure you can use your YAMAHA sound card at the same time.