Help with fatiguing sound in my PC system


I replaced my Halo Pre and Denon changer with a PS Audio DL III. I run lossless music into it from iTunes on a PC (Windows 7 64bit, core i7, 16MB RAM), I use a Pangea USB cable into a MF V-link, then go into the DAC with a Wireworld ultraviolet coax. The increased detail, clarity, resolution and extension are remarkable, but so is the amount of listening fatigue. The highs are too much, but the music sounds muffled if I add the pre-amp back. My system is profiled in the link below. I have some ideas, let the voting begin:
1 - buy an offramp or a pacecar (can't afford it!)
2 - use better USB/coax/interconnects/speaker cable
3 - apply acoustic treatments to the room
4 - use a software player (Jplay) that sits on top of iTunes
5 - buy speakers with different tweeters (Quad 22L2/Focal 826v, this is happening, but not any time soon)
6 - get a better amp (McCormack/Odyssey, distant future)
7 - tweak Windows 7/iTunes settings (WASAPI exclusive mode?!?)
8 - adjust speaker position/toe in (already did this and it helped a little)
I am thinking about trying #3/#7 next. Ideas? Thnx in advance.
realremo
There are so many variables. Impossible to say exactly what your problem is. However, in my experience, I've found the connection between the computer and the dac is a big deal. A poor connection equals jitter. Jitter equals fatiguing sound. I use a high quality USB cable and an audiophilleo. If I had more money I'd by a better reclocker. What that is I don't know. The wireworld is not a high quality USB. I use the top of the line ridge street audio USB. I'm sure there are others that are equal or even better, but that's what I use. In order of importance I'd say: 1. USB cable, 2. Reclocker/master clock. You need both to solve jitter. That's what I think.
My USB cable is a Pangea, but still, point taken. It will be a long time before I spend $600-$700 on a cable.
Realremo, I found that both USB and coax cable mattered but didn't spend a lot to get satisfaction. For USB I tried Audioquest Forrest, Pangea silver over copper and ended up with far better results from Pangea 24 gauge Pure silver.. better high frequency detail and imaging. Like wise Parts Connexion sells DIY Furutech components for FX-Alpha-Ag silver coax cable which I found bettered anything else for under $200, just some wire stripping and solder skill required for the termination of choice.