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It’s a two part numbering system. The first digit indicates the number of speakers (for example, the 4 of 4.1), and the second number (.1) indicates that there is a subwoofer. So, 4.1 would mean there is a front left, front right, left surround, right surround, and a subwoofer. 5.1 would be the same except there would be a center channel. 6.1 would indicate there is a front left, side left, surround (rear) left, front right, side right, surround (rear) right, and a subwoofer. 7.1 would be the same as 6.1 except with a center channel. I would pay more attention to the quality of the system than the number of speakers. I recently upgraded from a relatively cheap 7.1 to a very good 5.1 system and my new system is MUCH better despite having fewer channels.