"My setup sounds great when I'm outside of my room. When I walk in and sit down, my ears start ringing."
This shouldn't be too much trouble since you have small speakers. Move your system to another room and try it there. You don't have to invest a lot of time in setup, you just want to see if the ringing will go away in different environment. Along with some of the others, I'm not too sure what the problem is here. Given that your room is fairly small, its going to be essential that you figure if the problem is equipment related, or possibly the room.
If it turns out that you still get the ringing, I think you should look at your source. I'm not too familiar with your Lumin, but with computer audio related components, there's usually a lot of adjustments and choices. Since you are plugging it into a new preamp, you could have a gain related issue, or something similar. It may need to be reconfigured to work better with your new integrated.