I noticed my HP8 was very sensitive to ground loop issues. I have one spot in the house with a little system set up, and the HP8 would be super noisy there. The noise came when I plugged in RCA cables, even if those weren't attached to anything yet. Adding the Yulong P18 power conditioner fixed the problem in that spot. But in a different room, nothing I tried was able to get rid of the noise. In other rooms it is totally fine. Some amps are more picky than others when it comes to this type of thing. Also some tubes are more sensitive.
Interesting you should say that. I had ground loop problems with mine too and found it to be very sensitive to mains noise issues generally. I assumed it was a tube amp thing, rather than a HP8 specific issue. I'd also assumed it was partly that I live in an house with old wiring and noisy appliances in the centre of town.
When I had the HP8 running side by side with my v200 both would exhibit the ground loop problem, but the Violectric was far less badly affected. With that amp I could only hear the hum when the volume was turned up well beyond normal listening levels, and then not very loudly. With the HP8 it was clearly noticeable even at normal listening levels. Eventually I reduced the problem by switching from a mains powered DAC to a USB powered alternative (Meridian Dragonfly), then cured it completely by buying the iFi USB power conditioner. This not only cured the noise but dramatically improved the overall sound too - £ for £ the best upgrade I've ever made. I'm regularly astounded by how revealing and musical it is now. I also found cable placement made a surprising difference too.
When I had both I don't remember having a clear preference for either with my LCD2r2 that I owned at the time. However, I eventually decided that I didn't like the LCD full stop, which may have been why neither combination really impressed me. With the HD800 it's a different story.