I was encountering the same problem.
The method I found most effective was putting the Spider IV amp on demo mode (all the effects were disabled). You only get the effects produced by your HD500, and there shouldn't be any extra noise.
Connect as follows:
Guitar Out -> HD Guitar In
HD Phones -> Amp In.
To put the amp on demo mode, press the "Tap" button while you turn the power on.
And there you go.
The only downside to this is a comparitively lower volume.
You can counter that by increasing the main volume on your POD, or try putting it on Line instead of Amp.
Hope this helped. :)
