Need Help With a Bright System

My system consists of two NAD C 272 monoblocks, an NAD C 162 preamp, and an NAD T 532 DVD player. The speakers are Triangle Antal XS. My problem is that the system can sound pretty edgy and bright on many recordings, particularly rock and pop albums. One very noticeable aspect of this bright sound is edgy vocals that have exaggerated sibilants (i.e. ‘S’ sounds). I'm currently using a pair of Kimber Timbre interconnects between the preamp and monos, and Acoustic Research silver series interconnects between the dvd player and the preamp. I was using a pair of Kimber PBJs between the dvd player and preamp, but found the ARs to be warmer and better on the bass. The speaker cables are a pair of Straightwire Quartets, which I believe are plain copper. Does anyone have any suggestions on how to get rid of this bright sound? Obviously I wouldn't like to lose detail while doing so, but I understand that this may be a trade off. I'm willing to make a necessary upgrade, but I just want to ensure that whatever I chose to upgrade will definitely take away a lot of the brightness that I currently hear in this system. I know that using a tube amp instead of solid state would make a huge difference, but what else can be done?