There isn't just "one" way...
For example, I normally use the 2CM through my Mesa Boogie amp, but last Tuesday I went to work with my original band. For that, I still use the 2CM to the mixing board but changed the system output setting to STUDIO DIRECT, used both (stereo) 1/4" outs, and used the full (instead of just the PRE) versions of the amp sims plus some re-EQing to taste. But instead of using the 1/4" L outs, I could have used both XLR outputs. Or just the left (mono) XLR output. Or just the left (mono) 1/4" output (just like I do with my amp).
See what I mean? The method you use will depend on the exact equipment you are feeding the HD500 signal(s) into and what it is that you want to accomplish. And there will most likely be multiple ways to do it.
If phantom power is on, I'm sure that L6 did the right thing design-wise and that pin on the XLR connector is not connected to anything on the HD500 (so it won't matter).
And no, a DI box is not required.
Thanks. I am planning to use studio / direct, full amp model.
If i am using balanced outs, do I need need XLR to stereo jack cable?
what's the difference between the balanced and unbalanced outs then?
You can use XLR cables if your board has XLR inputs.
A balanced sound provides more shielding from electro-magnetic interference than an unbalanced signal does. For short cable runs you're not likely to hear a difference, but for longer (tens of meters) runs balanced signals are more robust and pick up less noise along the way.
One important consideration though is this: if you're sendong both L and R channels, you're fine. If you're using stereo effects, but sending only a mono signal, whereas plugging a single 1/4" jack into the live outs will give you a mono signal, using just the L or R side of the XLR out will give you the relative half of the signal (L or R).
Since most (smaller) venues are inappropriate for highly separated stereo signals, I find I often use the unbalanced out in order to send a mono signal.