Acoustics in the Room.... Bottom line I have had shrilly sound and very thin sound, make sure you have a full wall behind the listening position and the Speakers, Sidwalls are not that important, actually the further away the better getting rid of direct reflection and adding body to the sound on the outside of the speaker as well as between them, I recommend no closer than 2 feet to sidewalls if at all possible. Your room if in the wrong configuration or even not very well acoustically treated( via, carpet, wood(not too much glass and windows) etc.) then you will never get best results, many have complained of this problem with a Monitor of any sort between your speakers as well due to the reflections off it, so big screens can be a deterent as well.
I have moved shrilly speakers into other rooms onto full walls with nothing deflecting sound down the side walls and they sounded almost like the tweeter and upper midrange were cut out! So its simply possible you just have a bad environment. I would not be so quick to dump cables or electronics in or out of the mix, you seem to have pretty well regarded to the slight side of warm equipment(accept maybe the siltech stuff). Good luck, but move them first it works substantially if you find where they need to be placement wise in the first place.
I have moved shrilly speakers into other rooms onto full walls with nothing deflecting sound down the side walls and they sounded almost like the tweeter and upper midrange were cut out! So its simply possible you just have a bad environment. I would not be so quick to dump cables or electronics in or out of the mix, you seem to have pretty well regarded to the slight side of warm equipment(accept maybe the siltech stuff). Good luck, but move them first it works substantially if you find where they need to be placement wise in the first place.