Best Amp to drive my Apogee Stages?

The amount of watts is not the issue. It is the load the amplifier has to deal with. True, a higher quality amplifier will sound better, but the Apogee is a hard speaker to drive and it is the load that degrades the sound of the amplifier.

In fact, the amount of watts is the issue. The impedence of Apogees speakers, barring the Scintilla, is 4 ohms. So most amplifiers can handle that. It is their low sensitivity that precludes most amps because they will not have the watts to run the speakers at decent sound pressure level.

In the case of the Stage, the sensitivity is a bit higher than other Apogees and also the spaker itself will not play very very loud (althoug it is good enough for most music except very loud rock or large orchestral music). Therefore, a 100-150 WPC good tube will drive it very well to the **Stage's maximum cability**. Having 400-500 WPC will not help any further although will not hurt either.

In the case of other Apogees, a 100-150 WPC *can* drive the speaker for low volume (e.g., vocals) but not for obtaining a good sound pressure level. Hence you will need more power.

The Stage actually goes below 4 ohms and while this may not be a problem for your monster tube amplifiers it can be a problem for other amps. However, the point I was trying to make is that an amplifier's sound quality will vary depending on the load it is driving regardless of the amplifier's power rating. Even your tube amplifiers would be happier if they were driving a speaker with an 8 ohm load.
BTW, whatever happened to the electrostics speakers you were building?

One of my heroes in audio is Leo Spiegel, the genius at Apogee acoustics who designed the Fullrange ribbon spakers.

In an interview in July 1990, he said:
"In the case of the Stage, we set out to make a smaller loudspeaker, still with a good, accurate sound but with higher efficiency than our previous designs so that it could be employed successfully in a wider range of systems. 'The way I set out to achieve this was by concentrating the amount of ribbon conductor in the magnetic field. A small improvement was also made to the magnet arrays too, but the primary change was to the woofer and tweeter diaphragms, which have a conductor on both front and back of the transducer. Another important, change was to the cuts which transform the bass unit diaphragm into ribbons. The sinusoidal cuts are only practical with the photo etching process used for a relatively high volume model like the Stage since the process will cope with, any arbitrary shape of cut. The smaller volume models are cut by band, so only straight line cuts are feasible. 'The electrical crossover point is about 350Hz, but the effective acoustic crossover point is around 600 to 700Hz as the electrical network is only one element of the transfer function and the characteristics of the ribbon have an effect here too. The blending of the woofer into the midrange/treble ribbon is very gentle. Every time we try a very sharp cutoff, you can bear the sound of the two units as two quite separate entities. It has been the same with everything we have worked with. You can always say 'here's the woofer' and 'here's the mid/treble tweeter'. But gentle crossover slopes demand good overlap in the frequency response, or the technique doesn't work, the units must be well behaved if such slopes are to work successfully".

"The Stage has a very smooth impedance and phase response, especially in the midband and tweeter region which has incredibly smooth group delay characteristics. In this way we can achieve depth and imaging. 'The idea is that you should be able to shut your eyes and sense locations and see the orchestra. We have worked very bard to achieve this. If it doesn't do this, it isn't one of ours. You might find a good receiver of, say, 50 watts/channel output that drives the speakers well, but so what? I think that the fine detail and the quality of the Stage really demand a truly fine quality amplifier. Power isn't the issue here. Quality is. So although the Stage is more widely compatible than previous Apogees we don't condone the use of poor-quality ancillaries anywhere in the chain."

I have Apogee Slant-6. I had Adcom GFA 200, Classe CA 100, Krell KSA 50S previously, and use Conrad Johnson Premier 11A now. The CJ has more "you are there" and wholeness to the sound and expansive soundstage. Really musical and tactile. You can hear the vibration from the throat and the moistness of the teeth when listening to vocals. The best tweak was using RCA clear tops on the 6FQ7 driver tubes. My preamp is Wright Sound WPL 100A, his top of the line single chassis (with in board phono). I have one of three made. George Wright was from Kent, Washington. He died last year. His preamps are the biggest bang for the buck ever, if you can overlook the exterior aesthetics. This preamp replaced CJ PV 12A. the system sounds like it has a shot of 30 extra watts of power and drive, oomph, depth and clarity.
Since your speakers are fully ribbon, I would try the Classe CA 100. It is rated at 100 watts per channel at 8 ohms, 150 at 4 ohm. It is cheap on used market. It sounds way more musical than the expensive current crop of Classe amps. It has incredible bass, especially for its power rating. The amp sound and play twice as loud than a 200 watt (solid state) Audio Research amp.
Good Luck.
Greg
P.S. I am using JPS Labs superconductor interconnects. Very transparent, but very rigid. I heard at least 3 more feet of soundstage depth with these interconnects replacing the "junk" Straightwire Maestro.