What amp do I need to power my Acoustat 1100

If you want to use SS; find an amp with MOSFET outputs. They will maintain stability at low impedance levels. One can practically arc weld with some MOSFET amps. I used modded Hafler DH-500s with Acoustat Model IIIs(in the early '80's) with great success(was a dealer, back then). I much prefer tubes, but synergism with electrostatics is harder to reach. Here's a suggestion: (http://www.avahifi.com/root/equipment/amplifier/fetvalve_amps.htm) You don't mention your pre, but tubes would be nice there, and would give you the ability to tweak the system's presentation to suit your tastes.

If you want a great stereo (actually 'dual mono') SS amp for around $2500+ look for a Mark Levinson 23.5 (not a 23, a 23.5!) 200W @ 8 ohms, and worked beautifully into 0.7 ohms! of my MartinLogan CLS's.

If on the other hand you want a great tube amp which puts out a very "current rich" 90W/ch you can't go wrong with a McIntosh MC275 Mk IV or Mk V; which are now selling used within your budget.

You don't mention your pre, but tubes would be nice there, and would give you the ability to tweak the system's presentation to suit your tastes.

I think this has become a popular misconception. If you want to roll tubes to tailor the sound of your system, you need a tube amplifier. In a preamp (with the exception of a PHONO preamp), the tubes aren't used for amplification, and therefore have little effect on sonics other than adding a certain amount of tube hiss to the signal (even in the more expensive units.)
.

Ns said, "I think this has become a popular misconception. If you want to roll tubes to tailor the sound of your system, you need a tube amplifier. In a preamp (with the exception of a PHONO preamp), the tubes aren't used for amplification, and therefore have little effect on sonics other than adding a certain amount of tube hiss to the signal (even in the more expensive units.)" In my experience, I've found tube rolling worked wonders in quite a few pre-amps over the years(especially my own ARCs), and particularly in units with tubed power supplies. Voltage gain is the purpose of most tubes in a pre-amp(just as in a phono stage), and they are in the signal path. Any tubes used in a pre-amp(or phono stage) need to be screened and certified very low-noise, regardless of the unit's cost.
.

look for a used symphonic line amp or amps--I have used 3 diff ones with my modded spectra 33 and they are a great synergistic match

Rodman, I don't know which ARC preamps you've owned, but the later ones with onboard phonostages (like the SP-14) use a single tube for gain in the phonostage only. The other tubes in a "tube" preamp provide source input buffering -- thus leveling the (input impedance) playing field for the various sources. This makes it easier for all the sources (including phono after being amplified in the phono section) to drive an amplifier.

Further, because tubes are high impedance devices, many "tube" preamps actually use solid state output stages because of their low (versus high for tubes) output impedance. Why? Because the lower a preamp's output impedance compared to an amplifier's input impedance (1 to 100 is considered excellent, 1 to 10 is absolute minimum) the more faithful the frequency response to the original source signal, and the farther the distance over which you can run interconnects (even single-ended interconnects) without signal loss or noise pickup.

So Rodman, if you've "found tube rolling worked wonders in quite a few pre-amps over the years" I'm not saying you're wrong, but I'd like to know two things:

1.) What do you mean by "wonders"? For instance, rolling an ultra quiet tube in place of a noisy tube is not a "wonder" it's just common sense. The sonics really won't change because a preamp if it's any good will remain neutral. The sound will come through against a blacker background if the tubes are quiet; for a REALLY quiet background, a quality SS preamp is just the ticket IMO.
2.) Where in the ARC preamp circuit is/are the tubes in question? If they are in the phonostage, they don't count for this discussion, because that exception has already been noted. If they (actually "it") is in the power supply, you have to be talking about an SP-8 (introduced in 1981) which did have ONE tube in an otherwise solid state electronically-regulated power supply. All other ARC preamps before and to the present, had/have ss power supplies.

Certainly in some of the 'all-tube' (except power supply) ARC preamps, there is ample opportunity to try different brands/types of tubes, but even ARC is always talking about better performance in terms of lower noise tubes, not in terms of better sonics (i.e. frequency distribution, detail etc.) Of course ARC has the (dubious) reputation for making the most SS-sounding tube equipment there is ;-)
.