Did a jam on Saturday after work. Had to use up the XLR cables running mics and feeds to recording, so ended up one XLR short when it came time to connect the JTV+HD+DT25.
So, I ended up setting the HD500 into 'studio direct' mode, and ran a 1/4" from the HD500 out to the FX return of the DT25. Then had XLR out from the DT25 to the recording.
For what it's worth, you can get really good sound running your rig this way. It's not ideal, since you aren't taking advantage of the full-on Bogner switching L6Link side of things, but works great in a pinch, and for what it's worth the DT25 sends that signal just fine via XLR out when wired in only through the fx return.