I am very new to home theatre tech and need some equipment. I have four speakers in my home right now (two front, two back) and am looking for an amp and a front center speaker to match (potentially a subwoofer as well). The two front speakers are PSB Stratus Silver, and the two back speakers are Kef speakers, model 1033 (not sure what year, exact type, etc.) with 4 Ohms. I already have a Sony multi channel AV receiver STR-DH540, but one channel has stopped working. Everything I have is currently bought second hand, so information is limited. Do you have any advice? Also, if cost exceeds $600, would it be worth it to purchase a Yamaha - YHT-5960 Home theater system instead?