@Brady > First, there is no "sync" between players. He's got the 900nexus connected to the network and the mixer is reading the beat-grid information from the player with the loop. The roll effect is thus snapped (quantized) to the beat grid of the looping music.
To get a loop (sample) recorded and moved to another channel, simply engage the roll effect on one of the channels to sample it, then change the channel assignment of the effect to another channel (say you record from CH1 then change the effect channel selector to CH2), it will then playback on CH2.