Having not received any response (as most probably no one has tried this) I still wanted to give it a shot and try the SE34I.2+ as a headphone amplifier, directly connecting the headphones to the speaker binding posts.   After some research on Internet for not blowing the headphones (as well as my ears), I found the information in the following link:

http://diyaudioheaven.wordpress.com/tutorials/power-amp-adapter/

Looking into the specs of my Audeze LCD-2, I prepared a cable with DHLabs z-plugs, DH Labs T-14 speaker cables and the female TRS jack of a Grado adapter.  As for the tube set, I used a pair of RCA 5U4GB's, a pair of 6N1P's that I bought from Steve and a bunch of different output tubes including Siemens EL34's, Gold Lion KT77's, JJ KT88's and Tung Sol KT150's.  Steve had already told me that the KT150 would not automatically bias in that amp, but I must admit that they provided the dullest sound of all even though they have some amazing results in my Copland CTA 405 push-pull amp.  

After few trials, I decided to go with the Siemens EL34's, maybe due to the advantages brought by the Hazen Grid Mode.

Anyway, the amp drove the LCD-2's very easily and with authority with tons of headroom; I can turn to volume up to somewhere in between 9-10 o'clock and more would easily create deafining SPLs.

The results are pretty decent so far with very detailed and pleasant mids and trebles as well as very tight basses.  The typical characteristic of this amp (to my experience) with less bass is prevalent with the headphones as well.  I thought this was mostly due to my previus set of high-efficiency speakers with strong impedance peaks at bass frequencies.  Even though LCD-2 is claimed to have a flat impedance curve, I wonder if it is actually not the case, or if the amp is not very bass heavy.  When I tried the headphones before buying it, the dealer made me try it on a Macintosh amp with a good headphone output, but the basses were not very forward on that amp either.  So this might be the characteristic of the headphone actually.

The only other alternative I have in hand to test the headphones is the Hegel SUPER headphone DAC/pre.  I will check the cans with that and report again.  In the meantime, I am open to suggestions to improve the basses of the SE34I.2+.

But so far, I am very happy with the results except that the bass could be a tad stronger.  So I believe instead of selling my SE34, I have put it into very good use!  :)

Cheers,

Alpler

Continuing the thread, I had the chance to try the LCD-2 with my Hegel SUPER and it was quite fine in terms of frequency response.

On another thread, Steve mentioned that the amp is designed specifically for 4-16 ohm impedance loads (mainly for speakers), so lacking bass with a load like that of LCD-2's is quite normal.  He also recommended that unless one would like to use speakers as well as headphones, adding a 5 Watt resistor with values between 10-100 ohms to the positive of the speaker output should resolve the issue.  That will be my weekend project.

To be reported soon!  :)

Best,

Alper