Meridian Explorer Subwoofer Connection - How to?

Just bought a Meridian Explorer. It has two outputs, the line level I'm using to connect to my Jolida 102B. I'd really prefer to NOT use the speaker level outs from the Jolida to drive my sub and was wondering if I can make use of the headphone output - simultaneously - to do so?

The sub has two RCA line level inputs and of course volume and low-pass filter cutoff. I figure 3.5 mm stereo to RCA plus cable / adapter and away I go. Any other considerations? Like;

- The line level goes off when you plug in headphones?
- The line level outs are 180 deg out of phase with the headphone outs, as per internal buffering amplifier?

I was also thinking of running the DAC off a cell phone charger battery - given that it outputs 5V, by making up a special usb cable to do so. Any benefit to not using HP PC USB power and the battery instead? Thanks!