Keep 5.1 or 2ch stream?

I am ripping a DVD and there are two audio tracks: AC3 5.1ch and AC3 2ch.

I can only fit one on the disc without lowering picture quality. I only have a 2 channel setup right now, but may get surround sound setup soon. I assume the 5.1 track will have the channels mixed together to play on my system? Will this sound worse than the 2channel track that is provided?

Thanks!

well if you are backing up a dvd. . . i would stick with the 5.1 sound becuz well that is what DVDz are for. . .to bring you good sound and video. . .oh and how much would it lower the video quality. . .it should not make a noticeable difference unless you are very picky and want only the best. Well what prog are you using n e wayz. . .i would recommend using Nero Recode. . .makez the job very eazy. But yeah 5.1 soundz much better and it would not make the current system sound worse so do not worry about it