Couple of questions:
1. When you set your system up in the new room did you re-calibrate you settings using an SPL meter or the built-in YPAO?
In my own experience, I've found the YPAO (Yamaha) EQ as well as the Audyssey (Denon) EQ work very well in taming certain frequencies using the 'Front' or 'Flat' modes. In both of my setups, I found that these modes had very little boost added to them and mostly knocked down the higher frequencies. My secondary HT setup has paneling on the walls w/a wall sized built-in bookshelf directly behind the front soundstage, so this room could be fairly bright w/out any FR modification or changing room acoustics. If you haven't run the YPAO using the 'Front' or 'Flat' modes, I would suggest doing so to see if this helps. Keep in mind that it tends to set a fairly high crossover level (200hz in my case), so you may need to change this to the standard 80hz manually afterwards. I'm not sure if the HK has this option, but if so and you decide to switch them out, I would consider using it.
2. Have you considered implementing any room acoustic changes to help with the higher frequencies?
Something as simple as a semi-thick tapestry placed in the first reflection point(s) of your mains can help tame some of the highs you're experiencing in the new room. Not sure if this is a dedicated theater (don't think so from your description), but would it be possible to use any acoustic panels to help in this capacity as well? GIK Acoustics makes some fairly inexpensive panels that would absolutely improve some of the room acoustics.
Here's a review AH did earlier this year on these panels if you're interested.
Even if you were using the HK instead of the Yamaha, you'll likely still have some of the same high frequency issues as it sounds (no pun intended) as though they are most likely due to the listening environment and not the equipment.... -TD