If you love Harbeths, I have a hard time believing you'll like the HD800, at least not without over-the-top warm tubes. Have you heard them? I heard them a while ago, and was not impressed (poor Qualia 010 ripoff). The HD650 or HD600 are both excellent, cheaper, and may be more along the lines of your Harbeth's sonics.
Also note that while Rogue tube amps are great, their built-in headphone jacks will not compare to a decent standalone headphone amp, or integrateds with a reputation for good headphone jacks.
Also note that while Rogue tube amps are great, their built-in headphone jacks will not compare to a decent standalone headphone amp, or integrateds with a reputation for good headphone jacks.