First of all thanks a lot to feilb for helping me to get a basic understanding of all this.
Since I had defective 6n6p tubes I replaced them with a 1980s batch (also a recommendation of feilb) and not only is the channel balance back, the slight buzz also went away and I seem to have a clearer background now, some may call it blackground.
I rolled the ECC85 in the last few days and it tends to give the HD 800 a dark character with a more hefty low ned, however the rolloff removes noticable more "air" than the standard 6N1P. So far they are not to my liking.
Next up: EC88 (pretty expensive though) and? I'm up for a new ideas.