What to upgrade next?

The biggest improvement in your system will come from upgrading your speakers. The cables may add some sound changes but better speakers will open up a new world of sound. Not that I think yours are bad, but look up the line and you will get better bass, mids and high end which to me is the biggest improvement one can obtain.

Happy Listening.

I think you're getting a lot of misleading advice. There is absolutely no reason to replace your cables, nor add fancy power cords or line conditioners. You already have a great system and assuming you've set it up properly, it's sound will not be readily improved without wholesale changes. Changing cables and such may slightly change the sound, but it's unlikely to really improve anything. I have three suggestions. First, consider some professionally designed acoustical room treatments. Dollar for dollar it's the most cost effective money spent. Second, look at getting a high quality rack and speaker stands (Sistrum, Mapleshade, Solid Steel, etc.). Third, replace your CD player with either the Linn Unidisk or Teac/Esoteric DV50. Both players are universal machines that will playback any format which will allow you to run hi-rez SACD and DVD-A digital through your system.

I think Onhwy61 makes a great point.

You seem happy with the sound. And, if you are interested in upgrading, I would ask what area(s) does it lie? From there, we can offer suggestions in terms of pushing your system in the desired direction. It seems as if your source, preamp/power amp, and speakers are on the smooth and warm side, while the cable is on the detailed and fast side. May just balance extremely well, and not need upgrading at all.

I can't argue with addressing the room, it's often the most overlooked link in the chain...

Out of all the suggestions so far I would tend to agree with Bidkidz. I myself have went through a number of power
conditioners,cables,power cords,digital upgrades. And while
they have all made nice Improvments in the sound, Changing
or upgrading speakers in the line you already have will
make the biggest difference.

Upgrade the room. It will make more difference than replacing the whole system. Most sonic annoyances are created by the room, not the system. I have found the information available from Rives to be incredible. Check out http://www.rivesaudio.com and see what they have to offer.