can a headphone amp double as preamp?

I have been reading how some listeners are questioning the use of using headphone output jacks, connected with 1/4" to RCA cables, to thier amplifiers, to drive thier speaker based system. Reviewing some specs showed that output impedence values of many preamps are about 500ohms. This is very close to the output impedence of the ASL MG head mk III, it has the option of 600 ohms. My bryston 4bsst amp has an input impedance of 50k ohms. Could the ASL work? And what about the OTL vs the transformer switch when driving the power amp? Ya guys see any problems with this set up? I would love to see what my speaker system would sound like with SET and OTL preamplification, as it can be very fatiguing (no tubes). I think it was Wes Phillips that said in his reviews of the Musical Fidelity X-can v3 that it could possibly be used for a preamp.

Thanks for any responses.

I had read many of the reports of people using the headphone 1/4" jack to rca to run an amplifier, so I decided to try it. I have an ASL OTL MG head mk III. I first used the transformer output option. Everything sounded to be ok through the main speakers, but I didn't sit back to evaluate the sound just yet. My main reason for trying this setup was to smooth out my Thiel 2.3's brightness. Next was to switch from the transformer to the OTL function, something very bad happened! I have a Monster HTS 2600 which shows amps drawn and the present voltage. With the cd playing, after flicking the OTL on and the volume knob all the way down, the speakers were still putting music to the amp, no big deal I thought. Within the next few seconds the amperes drawn by the components rose to 4A ( I had not touched the volume knob). This current draw usually plays VERY loud when used with my current preamp (musical fidel a3.cr). Also the voltage drooped from 120 to 110, which has NEVER happened before. Fearing impending meltdown of one (or all) of my components I shut it down. After removing the 1/4" to rca jack and playing the system as usual, nothing seemed to be broken. I am not an electrician so I do not know exactly what was going on, but 4 amps going to an unknown destination with no significant volume through my main speakers was terrifying! I do NOT recommend anyone with an ASL mk III headphone amp to try this!