Hi everybody. This is my first post in the forum, mainly because i´m new to HT. I currently have a Logitech Z680 THX certified PC Speakers (they served me well great value). I´m looking into starting with a good receiver, and 2 front loudspeakers, and then going on from there. Room dimensions: 20 feet x 14 feet x 10 feet high. My options are Pioneer 815, Pioneer 1015TX (a lot more expensive here in Argentina) or Yamaha rxv657. I can get a very good price on the Pio 815. What do you recommend? also, are the Polk monitor 50 a good match for these receivers? Thanx in advance.