Traditionally, speakers like the Heresy did best with tubes. Its easy to imagine it being a bit harsh with a transistor amplifier. You don't need a powerful amplifier so you have lots of options. I would recommend something with at least 15 watts per channel. Our smallest amp drives that speaker with ease.
As I recall that speaker is fairly deep. So I would back them up so that the back of the speaker is only a few inches from the wall. That will help with the bass and due to the depth of the speaker, will not mess with the imaging.
I would also check the phase; simply reverse the red for black on one speaker only and listen to the result. If the speakers are out of phase with each other I can see the system acting very much like you describe!
Keep your speaker cables short. High end speakers do not deserve to have the cables in the wall! This will help regardless of the speaker.
As I recall that speaker is fairly deep. So I would back them up so that the back of the speaker is only a few inches from the wall. That will help with the bass and due to the depth of the speaker, will not mess with the imaging.
I would also check the phase; simply reverse the red for black on one speaker only and listen to the result. If the speakers are out of phase with each other I can see the system acting very much like you describe!
Keep your speaker cables short. High end speakers do not deserve to have the cables in the wall! This will help regardless of the speaker.

