So many great suggestions, almost seems pointless to add more and pardon me if I am redundant in my suggestions but here goes.
The very first thing to do is play with speaker and listening position placements. Set that up first but after my second suggestion you should experiment with speaker location again to fine tune them.
Second thing is to begin to add sound treatments that will both absorb and diffuse the sound as it moves through the room. Your room is large enough to properly use diffusion. These panels need to be at least 6 feet from the listening position but more is better. They typically should be placed behind you but you can experiment. Bass traps in the corners are a great help and absorption panels on the side walls right in front of the speaker to absorb those first reflected sound waves is very important.
Make sure you have plenty of space behind the listening positioning and the speakers are well away from the front and side walls. The equilateral triangle positioning for speaker and main listening position is a great suggestion, but does not need to be exact. More important is to have the speakers away from the walls and your listening position away from the back wall. Make sure the side and front wall measurements to the speakers match each other, very important.
Next as many have suggested your DAC may or may not be an issue. Try taking it out and see if the sound improves. Use a record player or a CD player, but do not run them through the DAC. If music does sound better that way then you may have found the next item to upgrade. Finally I do not know if your amplifiers are a good match or not so call around to a number of dealers who sell your speakers and ask them for their recommendations. You might even drop the manufacturer an email and ask for their recommendation.
Once the above has been completed I believe you should be very happy.