Are you sure you hooked up the sub to the "Sub Out" RCA connection on the back of the 3808? This should be connected directly to the sub "line in" without a splitter.

LFR1100 Actives,QS10HPx2,QS8x2,EP800,M3x4,M3x2 (Wood),M5HPx2 (Wood),AxiomAir,ADA1500-8,ADA1500-7