What should I upgrade next?

Zaikesman...thanks for your great elucidation of what I was clumsily delineating.
KT88...OF COURSE it's GIGO, but in absolute physical terms
(freq response, coherence, temporal/phase stuff) that are readily discerned, there is MUCH greater variability in the speaker-room coupling than in the sea of Redbook players.
And in the thread-head's case this is most apparent: his Nak CDP is in most ways much closer to supplying a musically-satisfying signal than his ADS boom-cha speakers are!
BowBow...the Acurus and ARC were recommended by NAD dealers as upgrades! Certainly the ARC sounded better, but the ACURUS was a gritty mess. The Alephs of course are another realm. I can't imagine that Lance's satisfaction with the ADS speakers will be improved with a more transparent amp!
Have you ever heard these speakers? And what if he buys a nice low-medium power high output impedence "sweety" and then tries it on the Maggies he just dropped on the thread?!
You really have to think of the speaker as a LOAD that must be properly DRIVEN. You don't build a car around a motor; you pick the motor appropriate to the load it must lug around, no?

Lance...if you try the Maggies then you WILL have to exercise care in setup and room-damping issues before you go preamp-hunting. I'm not sure I'd pick a tube pre next as the 2600 is colored enough to affect that decision too. As well impedence-matching issues may result in frequency response anomolies that could make your decision-making a bit complicated, and thus frustrating.
Get your speakers, then try to audition several pre/amp combos. If you're not sure, then at least try to use one you like long enough to audition several fine front ends.
The 2600 simply won't quite be transparent enough to make CDP comparos as easy as a great amp (and pre) will allow.
KT88's certainly correct here.
I'd focus on the amp chain as a WHOLE once you get the speakers selected. THEN get a real front end and your jaw will drop! Have fun.

ho hum.............. I'm getting bored. I bought my speakers last in my system, and it sounds wonderful!

All you who are saying if you were going to build a system you would start with the speakers are totally missing the point. The original poster just wants to do one upgrade; not completely rebuild the whole system.

Sure; if I always wanted a pair of Nautilus 802s, I would start with them and then choose the electronics. But if I already have a system and can only do one upgrade, what good is a great pair of speakers being driven by inferior electronics? It would sound like hell.

We'll argee to disagree, Kt88, although I certainly acknowledge the possibility that you built a satisfying system in your own way - mine is not the only way (and mine is also definitely not the best system out there, and never will be!), but I do think it's the most logical and predictable way. Listen on, brother!

For the record in this thread, Magnepans are not electrostatic speakers, nor are they ribbons, in the case of the 1.6's. They are planar-magnetic speakers, combined with ribbon tweeters only in the models with the "R" suffix. The confusion tends to arise because all of these types are frequently (but not always) configured as boxless, dipole radiating, panel-type speakers, but they do employ different operating principles. (The Maggie models with the "QR" suffix are designated "Quasi-Ribbon" for the tweeter, which is roughly speaking like a cross between a planar-magnetic driver and a true ribbon driver.) The following is my admittedly non-expert attempt to explain these differences (corrections welcomed where needed).

In a true ribbon, the best-known examples of which (aside from the Maggie "R" tweeter) are probably the late, lamented Apogee's, the driven membrane is a metallicized film that is itself the conductive element of the driver, much as the voice-coil functions within a regular dynamic driver. In a planar-magnetic design, such as the mid and bass panels of all Maggies, a thin-film membrane is embedded with a wire running through it that functions as the conductive element. Both of these design types employ fixed magnets to drive the membrane when current is applied to the conductor, again much as in a dynamic driver. In an electrostatic design, like a Quad ESL, Martin-Logan, Sound-Lab, or InnerSound, no magnets are used. Instead, a thin-film membrane is suspended between two perforated (for sound propagation) conductive metal elements called stators. The speaker must be plugged into the wall AC, to supply power that is used to impart the membrane with an electrostatic charge when operating, which does not vary. The stators then carry opposite phases of the variable alternating music signal from the amplifier (after being converted from current to voltage by an integral speaker input transformer), which causes the stators to alternately attract and repel the statically charged membrane, producing the diver's motion.

For reasons that I don't fully understand, panel drivers of the planar-magnetic and ribbon varieties are typically not run full-range, but crossed over using separate, frequency range-optimized individual drivers to handle the complete spectrum, while electrostats are in principle single-driver, crossover-less, full-range transducers, but in actuality are often crossed over to a dynamic-cone bass-range driver for practical reasons having to do with maintaining a manageable panel size. Also, ribbon tweeters have often been employed to handle the treble range in box-type, otherwise dynamic speaker designs, such as many historical Infinity models that utilized their EMIT ribbon tweeters, or newer models from Piega or Red Rose, for example.

Sorry I ment Planar speaker. I have lusted for the maggie sound for 10 years, but I am open to others that compete in that price range.

Thanks