The Mac 1900 has Main-In & Pre-Out jacks..
Use Y adapters, 2 male RCAs to 1 female RCA..
Next run cables (L/R RCAs) from the female RCAs into the subwoofer, set the subwoofer X-over @ 100Hz and Sub Level to mid-point.
Fire it up and tweak the Sub Level control if necessary..
Just my $0.02...
