I was breadboarding a two-stage 6SN7 amp, intending to use some Lundahl iron for impedance matching to 600 ohm Beyer 'phones.  But I wanted to use the headphones while putting the amp together, so I tried a cheap trick:  I used the output from my preamp straight to 1660 transformers to headphone jack with clipleads.  Kinda goofy but sounds pretty darn good!  Then I used some 1680 transformers (more inductance) instead, and thought it sounded a bit better.  If you have high output from a preamp, and high impedance headphones, and have some appropriate iron, it's worth a try.  For the 1660's I used the Alt Q wiring, and for the 1680 I used Alt B.
 

 

Neat! its nice to see people coming onto the boards who like transformers. 
 
I have done similarly to this with autoformers from Edcor. 
 
If everything lines up properly (voltage levels and whatnot) try plugging the transformers directly into your source - skip the pre all together. My setup would not go less than about 80db with Beyer T1, but it was a fun experiment and sounded quite nice ignoring the kind of silly SPL.