I'm sorry if this is the wrong place to post this. Please move it if I erred... I currently have a PC with an Audigy2. It's hooked up to a 2 channel Harman Kardon amp that drives two JBL E50s. I have a cable with a 1/8" stereo plug on one end and two RCA plugs on the other end going from the speaker out on the sound card to the amp. Works great. Loud. Good sound (as good as my square, crappy room will allow). I want to add a subwoofer to the mix, plus a new Sound Blaster X-Fi XtremeMusic sound card. The sub will probably be a JBL E250P-Z. I'm not sure how to hook this all up, though. I experimented a bit with my SVS and couldn't get it to work right - sounded terrible. Do I need the two-channel amp anymore? Do I need this thing or this? What if i want to do 5.1 later? TIA.