How can I use 8 samples in one channel and not just 4 samples
Every remix deck has only four channels. For eight, you will need to use two remix decks.
Every remix deck has 4 slots (sub channels) with 16 cells each. Every slot can play one of it's 16 cells at the same time, so only 4 samples per remix deck can be played at the same time. If you want to play 8 samples at the same time you have to use two remix decks.