I'm planning to buy a 4-speaker output 3D soundcard (e.g. SBLive) and I currently own a pair of Altec Lansing ACS48 with subwoofer. Should I buy another pair of speakers for my soundcard to get better 3D effects? If so, is an ordinary cheap pair of speakers enough for the rear? Or should both front and rear speakers of equal quality? What if I buy another set of ACS45 for rear, or even worse, use generic multimedia speakers? The ACS48 has already burnt a hole in my pocket and it'll cost me a fortune to buy another set. Any suggestions?