Frustrated with the sound of my system

I disagree with all the room comments. Yes room can make a difference, but you cant put lipstick on a pig. I would not give it that much weight for performance improvement based on what you said. The next place I would check is the amplifier. Not sure your budget, but you probably need something newer and a lot more resolving to get your "air" while at the same time being smoother on top that would not be so irritating. Try an older Musical Fidelity A3CR, Pass Aleph3 or Aleph 30 and dump those Kimbers for whatever you can afford at Morrow Audio.

Arbuckle,
You aren't on board with what is considered axiomatic in hifi circles:
A GREAT system is a poor room is outgunned by an OK system in a GREAT room?

The speaker is what everything plays through. Chances are, if you get a speaker to your liking, the system will be easier to build.

If you like the Maggie sound, I think buying a pair of Maggies is a step in the right direction.

Also, be sure to get out and listen to equipment when you can. I try to make two or three outings a year to different cities to hear new offerings. You obviously have to decide.

It took me many iterations, time and money to get the sound quality I was looking for from my system. I found one key issue is the mains wiring, and in particular power supply grounding i.e. are all components grounded or should only the preamp and/or amplifier be grounded. However do be careful in removing the earth connection to a component - first check the manual whether this is a potential safety risk.
The other issue may be the loudspeakers - in particular the tweeter. I don't know what drive units you using, but it took decent and pricey loudspeakers for me to get the combination of detail, air and smoothness I was looking for in the highs.

So my suggestion for debugging your problem is to borrow a recent released good modest CD player (e.g. Marantz or Cambridge Audio), a good integrated amplifier (ditto) and a decent loudspeaker (that is relatively easy to drive from modest integrated amplifier). Ideally you should hear these components perform in a different system to the level you expect. Then swap out these with your system one at a time until your find the problem.
I recommend an integrated amplifier because that limits the power supply connections. Also I recommend that CD player and amplifier are from the same company so that you minimise risk of incompatible power supply grounding.

If none of these solve the issue, then look at the mains quality and then the room acoustics.

BTW, I have previously successfully used Kimber 8TC - they are unlikely to be the cause of hard stringent sound.

You have quite a conglomeration of components and cables going on there. The fact that you are unhappy with the sound is a perfect example of buying recommended components without knowing how they will work together. This is why, when in doubt, it is better to stay with like brands of various components since they are designed to work together. Your SFL-1 is known to be on the forward/thin side and I have no idea how it mates with the Classe, but the Classe amps I have heard after the DR series sounded less then full bodied to me.

For starters I recommend trimming your system down to locate the problem. Take the subwoofer and DAC out of the system and just work with the basic system. Try a warmer tube in your preamp and experiment with different cables before changing components.

Without knowing a single thing about the room or how the system is set up in the room a recommendation for room treatment is absolutely rediculous.