Help. System sounds thin and bright or harsh

I'm not familiar with your speakers, but FWIW since you're moving them around....

IME, floor and bass driver interface (distance between the bass driver and the floor as well as the side walls) goes a long way in determining bass reinforcement. I think someone suggested tilting back your speaker already but lowering your speakers height, which may seem counter intuitive, off the floor in combination with the tilt would make a better bass response. What I would try just to see if lowering the speaker would help just get them up about a foot off the floor (and tilted back so the tweeter axis is pointed at your ears). And go from there. BTW if you want to keep the sense of depth of image keep them as far away from the back wall as possible.

In my room traps and absorbers behind the listening position did not work out so well. 

Scott, @verdantaudio, mentioned it above. Swap components out.  Doesn't the Oppo have volume control? Or does it get disabled with the mods? If it still has the volume control remove the preamp and see how it sounds using the Oppo as the "preamp". I find it hard to believe there isn't something else going on with either a component or the speakers so I would sub out preamp first, then amp (if you have anything at all, even an old receiver) then sub the source. I have those Harbeths and have used Pass stuff with them. You could use dental floss as cables and it won't sound as bad as your saying. No way any decent quality cable will make that huge of a difference unless your listening at like 110dB. There's something else going on.

OP- are you measuring the back or the front of the speakers from the front wall?

@cymivka,

The DAC is the Musician Aquarius. There's some reviews out there but not a whole lot. If you watch the youtube review by Tharbamer my dac is the actual one in his video as I made some trades with him.