Since you've got pretty similar gear to me, did you ever try this?
So I've got my HD500 and Triple Rectifier working together using the 4 cable method. I then turn the output of the amp head to pretty much zero. It still has a small sound coming through the power amp, but it's negligible. I then take either the headphone out or the XLR out of the HD500 and run it into my recording board. I now have my pre and post effects along with the Mesa preamp sound going direct, with no adverse affects to the head in doing so.
I didn't know if you'd tried this before getting the now infamous cab clone, but I'm getting better results than miking the cab by doing this.
For example, here's a clip of the triple rec direct fairly dry, into IRs and with some EQ:
Here's the same guitars in a rough mix with the other instruments: