I'm not that familiar with your specific components so I will limit my comments to general ones. Although cabling and power conditioning can certainly make a difference, those differences are more about fine tuning. If you are unhappy with the overall performance/sound of your system, a change in cables or conditioning is not likely to make a leap that would overcome that kind of dissatisfaction IMO. I do think your suggestion about the room could have more impact, but not knowing how bad it is, that would be hard to say. Treatments can be as wife-friendly as carpets, wall coverings and plants in the right places. Speaker positioning also can have a pretty significant impact on presentation. Have you tried playing with that? Just looking at the list of your components my knee-jerk reaction is that if I were to work on one of them it would be the preamp. Seems like the others are proven performers at the top of their class, whereas the pre is a DIY unit that seems a bit outclassed by your other components. The preamp is a very important part of the chain so I might start there. Again, that is just a gut reaction - I have no direct experience with any of your components.
Marco
Marco