This isn't necessairiy specific to the HD500.  I use an X3Live, and sometimes my pedalboard with a real amp.  Here's the "recipe" that I use.

Start with the delay model that sounds best to you.  I use the digital delay, but some folks prefer analog.  I do not use any of the stereo delays, as I am using mono output

Place the delay after the amp

Dotted eighth setting

Tap tempo to song tempo

Feedback = between 30% & 35%

Bass = around 35%

Treble = around 25%

Mix = 30% to 38%

Add more "feedback" if you need more echo trails - Add more "mix" if you want the echos more pronounced

Adjust the "bass" and "treble" to suit your guitar; less treble for single coils, a bit more for humbuckers.

Depending on the room, maybe a light touch (less than 15%) of reverb placed after the delay.  I also sometimes like a very light touch of analog chorus placed after the amp for slower songs.

That should get you pretty close.  Use your ears to get you the rest of the way.  I've been playing on a worship team for five years with a recognized, world-class worship leader, and I've learned that nailing the exact tone isn't nearly as important as providing an atmosphere in which the Holy Spirit can do His work. 

Blessings,

Charlie