Reply to Low Input and skipping message

Hi newbie here,

Need insights what causing low input and skipping message. Im using s4 and mk2-1210 and macbook core2, 4GB ram, TSP 2.1.2 mk2 vinyls.

Been trying to setup my s4 as a mixer for 2 track decks and 2 decks in timecode but no luck, set A and B deck as track deck. Deck C as track deck and D scratch control. Gurus is this possible? 3 track decks and 1 deck for scratching purposes. I tried but low input and skipping and cross fader does not work.

TIA