I've done a comparo between the Bolder w/Silver Eichmann's (performs better than the copper Eichmann's, but not as well as the Copper WBT NextGen's) and the Stereovox.
Don't recall what thread I posted the results in. You can search for it to get a more detailed telling of the results. But the Stereovox didn't work in my rig. The Bolder w/Silver Eichmann's was almost (and it was very close) as detailed & noiseless as the HDXV. But the HDXV was painful to listen to (quite literally) for more than 30-45 minutes. The HDXV is the only digital that's been like that in my setup. I've used digitals that were cleaner than the HDXV, but didn't kill my ears. Can't explain why the HDXV acts like that in my setup.
I'd imagine that the Bolder with Copper WBT NextGen's would be as clean or cleaner than the HDXV, but not be painful to listen to. The Silver NextGen's are even better, but cost even more than the Copper NextGen's.