Isn't there some kind of output booster I can hook up to my amp to use with a converter?
As far as I know, you cannot use your existing headphone amp with electrostatic converters. Aside from lacking sufficient power, there is different technology involved, and attempting to do so could damage your equipment. I think it's because the converters require a lot of current, which speaker amps provide. There are plenty of cheap speaker amps out there, though most people who own dedicated electrostatic headphone amplifiers insist that they sound much better than with a speaker amp and converter.
Here's a little insider info, though, in case you ever decide to get 'stats.
The SR-009 and most other STAX headphones have an optimal power input (as in how much power it needs before the sound quality stops improving, at which time more power would just yield more headroom) of 900 Vpp. For the SR-007, it's 1,100 Vpp.
Background info about the voltage specs:
Vpeak to peak is defined as the voltage measured between the maximum Positive and Negative Amplitudes on the sine wave.
The Vrms is defined as square root of the mean of the squares of the values for the one time period of the sine wave.
Following is the formula for Vpp to Vrms conversion.
V
rms = 0.3535 * V
pp
And here is a thread with voltage ratings for some of the amps:
http://www.head-fi.org/t/582518/electrostatic-amplifiers-voltage-ratings
I'm not quite sure about the current (as opposed to voltage) requirements, though. The most common amp people say is the best for the SR-007 is the BHSE (HeadAmp Blue Hawaii SE), which costs $6-7K and has a very long wait period (some people waited over two years) after a 1/4 deposit. But that's just if you want the cream of the crop. Some 'stat amps with enough power are much more affordable.