Originally Posted by Sherwood
That, good sir, is nigh impossible without an EXTREMELY powerful headphone amp. Think whole watts. You're looking at thousands of dollars.
Well, hundreds anyway.
Stax transformer boxes need at least a few whole watts. Most of them seem to be rated for a maximum continuous power handling of 5 to 7 watts.
This means that only the more badass of solid-state headphone amps can be configured to do the job.
A maxed out M3 should be able to do the job - it will do 6 watts RMS into 8 ohms with a big enough power supply according to AMB. This can be built for $200-$350 depending on how frugal you are.
A B22 with a similar 3.5 amp or so power supply should also do a fine job, and will cost a lot more than an M3 because it's a lot more complex of a build.
Some people do drive their stax transformer boxes with a Super T-Amp, which works, but probably not as well as a good speaker amp.
On the whole i have to agree with Sherwood that the ideal low-cost solution is a vintage integrated amp, or perhaps a vintage power amp driven by your favorite headphone amp (used as a preamp)
The actual power requirements aren't very high. The SRD-X is literally a transformer box driven internally by a pair of car radio chip amps that aren't even heatsinked. It's powered by 8 C-cells. It works just fine, but a T-Amp + SRD probably sounds better.
Another suggestion - a JVC "executive" office/bedroom stereo. Or a more modern version of that sort of thing. I have a Philips MCD708 mini-system that drives an SRD-7 in a pretty ok fashion and includes a dvd player, am/fm tuner, and pretty reasonable speakers for under $100 all over ebay recently (mostly refurbished units). No headphone jack, though. I'm still investigating whether an external headphone pad hooked up to the speaker amp is likely to work well (can only safely be done on single-ended amps).