What should I upgrade next?

No component you buy is going to impact and define the sound of your system more than the speakers. While electronics are critical to getting the most out of your system, if your speakers aren't capable of resolving enough or don't produce music in a way that really moves you or connects you to the music, no level of electronics is going to make that happen. Get the speakers right and the rest will follow. I'd agree that the preamp should be next on your list. Best of luck.

Tim

Let's try a little example here. Given $3-$4k to spend on this system let's say you can put it into the source or the speakers. I don't care what source you put into this system, my contention is that I'd much rather hear this current system through a pair of Silverline Sonatinas or Vandy 3A sigs than the ADS speakers with an Ikemi or even a used Audio Aero(same would hold if the amp or pre were replaced instead). Get the speakers right and the rest will follow. Improving electronics will surely improve what you hear out of your speakers, but they cannot change the physical design and overall character of a speaker(hence the example above), which is why you should get that right first. Best of luck.

Tim

I thought it was interesting you happened to mention Maggies as a potential speaker choice as I couldn't think of a better example of why you should pick speakers first from a practical system building perspective. Ribbon speakers(which I believe the Maggies are--not electrostatic like Martin Logans) can present a very tough load for an amp, and if the amp isn't up to the task you'll never get the magic the Maggies can produce. It would be a shame if you flipped over the Maggies and found out the amp you just bought isn't suitable for power-hungry ribbon speakers(a lot of amps aren't)--your choice would then be sell your amp or forget the Maggies, neither of which is an attractive option. You just inadvertently pointed out one of the major reasons to choose speakers first(also one of Zaikesman's points above). Best of luck and have fun.

Tim