It depends in the model of your sub, but the SF3 has two pairs of pre outs, therefore, you can connect the sub via the pre outs.
5 responses Add your response
I used to have SF Line 3 and SF Power 3 combo. One pair of XLR output from preamp to power amp and another pair of XLR from preamp to two Velodyne DD12 subwoofers. Velodyne DD series is good because you can easily adjust the equalization curve to suit your room and the remote control can allow you to adjust the volume without leaving your chair.
Before you do anything suggested, we need to see if you get a good impedance match with all this.
Your SF3 is tube and may not be a great impedance match with the combined load of your main amp and both subwoofer amps, and you may not get the best of your system.
To see/calculate this for you I need to know.
1: The output impedance of the SF3
2: The input impedance of the main amp.
3: The input impedance of each sub amp.