Asymmetric Room

@OP While not necessarily the cause of your problem, you will get comb filtering from reflections from your sofa as well. So a throw on it will help as well. If you are hearing the problem within a foot of the speaker, check that it's not a resonance in the speaker itself - check that all the drive units are properly torqued.

It's often overlooked but adjusting speaker rake (tilt front/back) can make a big difference in treble response.

I tried having both a pool table and stereo in the same room and I ended up selling the pool table, because there was no place in the room for a sweet spot.  Also, I use the stereo 10 times more than the pool table.

@signaforce covering the TV will most likely not solve the issue. 
I would try:

1. Toe in more towards listening position - this will minimize reflection on the right from the window 

2. engage the warm filter on the Qutest DAC. I remember this filter being my favorite when I had the Qutest

3. Try different digital cable. Not sure what cable you’re using now. I liked Audience USB on Qutest. 

@audphile1 Thanks!

1. The room has 8 windows, 4 on the right. As you saw there is a tall couch, multiple pillows and an acoustic panel. Everything I can do this side of heavy curtains. Played with toe in, will try again. 
2. Have been using incisive, as I prefer crisp & lively, will switch. 
3. I am currently using Cardas Clear USB, which recently replaced my XLO ultra plus.