Hi,
Here's my own advice.
First of all : if you think your system works superbly, don't change it. What you should know is that upgrading one element might stress the weaknesses of another and soon you'll find yourself looking ofr a new change... So, if you like what you have, think twice before changing anything. By experience, I know that, reaching a level like yours, each significant improvement will cost a lot of money to be fully effective.
Second of all : you should really think of what direction you're headed. For now, you have a stereo system. But what if tomorrow you're thinking of Home-Theater ? Why that consideration ? Well, that is a determinant for your source and control choice...
Third of all : a CD192 ? Good player but find one used for a really low price. Less than 300£ I'd say. Remember that the new CD17 and CD37 are out and the CD17 is 500£ new. And the CD37 1000£ new. For the CD37, that's about the price of the CD192 new and it adds the SACD playback ability.
Fourth of all : as stated in some other posts : try out minor tweaks (sorbothane feet, spikes, cables...). That may be worth the money. And you'll be able to keep those even if you change your gear later...
Last of all : speakers change will affect the sound greatly. But remember that speakers cannot recreate information that has been lost by the amplifier ; and the amplifier cannot recrete information that the pre-amp has lost ; and a pre-amp cannot retrive information that the source doesn't give him. For now, your system is coherent, and that's what makes it sound good. If you want to improve things, you should in fact begin by the CD player, then the pre-amp, then the amps and then the speakers, even though you might be tempted to change the speakers firts, as that change will give the more audible results.
Regards.
PenguinHiFi