Yes, you can still sample from a record player with the 8-outs. It doesn't affect the inputs AT ALL.
What the 8-outs does is let you assign each sound out an individual output (instead of the stereo outs) for tracking/recording. If the sound is stereo, then it will take up 2 of the eight outs (one for the Left channel and one for the Right). And obviously you can only buss 8 sounds out at a time max., but the point is to isolate each sound to it's own output and therefore it's own track when recording to a multitrack recorder. Then you can sync up the MPC with the multitrack, and buss another 8 sounds out again.
Example: on your first pass, you can buss your kick drum out on 1, your snare on 2, hi hat on 3, congas on 4, some stereo pianos on 5 & 6, etc., and a stereo trumpet on 7 & 8. then your second time around, when the MPC is synced to the multitrack, you can buss a clap out on 1 (but going to track 9 on the multi), etc. etc. etc. etc.