There is a tape out on the NCSE which should work fine for line level if that's the way you want to run your subs.
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Sorry, but the tape outputs are NOT controlled by the LFD volume control, so you would have to adjust the level on the JL F110 every time you would change the volume on the LFD. Hence, not a solution.
Unbalanced RCA type inputs are always line level. Unfortunately the balanced inputs on the Fathom are also line level; the manual states:
"CONNECTING YOUR FATHOM Balanced Inputs
If your home-theater receiver or preamplifier/processor provides balanced outputs, the Fathoms balanced inputs are the preferred connection."
If you are planning on keeping your LFD, you either need new subs, or explore if a reputable modder can install pre-outs on it.