[kramer5150]

Something I have always wondered....
 
Can I use two separate stereo amps to power one headphone?
 
Using a Darkvoice 336 as an example, because I am familiar with its bigger brother 337 having owned it for a couple years.  The 337 I think is just two 336 circuits running dual mono in the same chassis.  The 337 parallels each triode in each 6AS7G / 6080, for the R and L channels.
 
So could I take the R/L line outs from my source, split each into two equal signals with a parallel "Y" cable.  So I'd have a Right-Y and a Left-Y to plug into a R-336 and a L-336.  That gets amplified by each 336 dual triodes, and results in essentially two Right and two Left channels at the 1/4 stereo TRS jack.
 
A headphone + cable like the HD650/600 would have to be re-terminated with separate Right and Left 1/4 Stereo TRS plugs.  Each plug tip & ring internally connected in parallel to sum the output of each 336 amp channels into each R/L headphone channels.
 
Would this work?

 

[nikongod]

Look up Fitz's work with the DV336. He ran them balanced, but the general idea is close to what it sounds like you are describing. 
 
You could also build what you are describing, single ended, but there are some pitfalls.
 
I think its a bit weird, that it is easier to make something balanced than single ended in this case, but that is what it is.