Subwoofer connectivity question

The input impedance of the line-level inputs of most subs is too low to be optimal when driven by a passive preamp such as the Lightspeed. Also, if the sub is not located close to the Lightspeed the capacitance of the interconnect cables that would be involved stands a good chance of being too high to be properly driven by the Lightspeed.

Splitting the output signal of the DAC, as was suggested, is probably a non-starter because you would have to adjust the volume controls of both the Lightspeed and the sub in sync, every time you want to change volume.

My suggestion is that you choose a sub having speaker level inputs, and use those.

Regards,
-- Al

Should I run leads from my amp to the sub, at the same time as running speaker cables from my amp to my speakers?

Yes. The input impedance of the speaker-level inputs of the sub will be very high. Therefore it will present a negligible load to the amp, and the wiring between the amp's output terminals and the sub doesn't have to be heavy gauge speaker wire; much narrower gauges will work fine for the sub connection too, as long as the main speakers are connected directly to the amp with heavy gauge cable.

REL subs, for example, come with a narrow gauge 3-wire cable which can be used for that purpose, one wire going to the left channel + output of the amp, one wire going to the right channel + output of the amp, and one wire going to the - output of either channel. (Connecting to the - output of the other channel isn't necessary, as the two - outputs of an amp that does not have balanced outputs are presumably connected together within the amp).

Regards,
-- Al