If you are talking speaker cable, then it will work just fine splicing. Just pick up some bog standard speaker cable and splice it in, hopefully it will still look okay to you.

bad idea, RCA uses an impedance of 75 Ohms, which you fuck up when you splice the wire. I'd recommend using RG6 cabling for the video, and, if possible, S/PDIF for the audio, but in lieu of that I'd ...