The Shure SRH840 was my first fullsize headphone purchased through my exposure to Headfi so they have a special place in my heart.  I have done some minor mods and made various cables over the past couple years, but I have finally finished my complete mod:
 
- Rewired (for the second time) with 26awg UPOCC stranded copper in clear teflon
- Proprietary locking jack replaced with standand 3-pin mini-XLR jack
- Removed most of existing headband construction and replaced with new pad
 
As a result, they are lighter, more comfortable, stay on my head better when moving around (they had a tendency to slip forward), look slightly snazzier with the copper wire, and are super easy to recable now (aftermarket AKG cables fit, not that I buy cables premade).  Thank you to the numerous Headfi'ers that have helped me with advice and inspiration.
 
 

 

There's a world of difference once that rubber headband is taken out. Just a great headphone.

Agreed on both parts.  Have tried many headphpones since and these still hold their own for me as a closed pair.  They still look a little funny on the head, but short of completely transplanting the drivers and housing to a new bad, there is nothing I can do about that.

Quote:

fraggler said:

Agreed on both parts.  Have tried many headphpones since and these still hold their own for me as a closed pair.  They still look a little funny on the head, but short of completely transplanting the drivers and housing to a new bad, there is nothing I can do about that.

Click to expand...

 
What do you mean by "bad"? Headband? How does it look funny? 
 
If it's practical and comfortable, then who cares if it looks "funny". All headphones look funny when you stop and really think about it. These aren't beats, so I'm guessing you're not using them as a fashion statement. 
 
Either ways, you did a great job on those. The mini XLR jack looks like a very clean hack. Do you have pictures of the inside? I'm curious as to how you mounted it.

Yes, headband.  I didn't spellcheck.  I have always felt that the SRH840's headband spreads out more across the top of the head and is much more prominent that my other headbands.  Other headphones I have conform to my head so that you notice the cups before the band, not the other way around.  I don't wear these out and about so it doesn't really matter.
 
The mini XLR was a pain in the ass since I didn't have the proper tools to do it nicely.  I basically hand made the hole from the existing one using sandpaper.  Didn't have a drill or rotary tool at the time.  So friction and a lot of hotglue is used.  I did the mini XLR over 2 years ago so the glue has a nice yellow tint now, but it is still as secure as the first day.  
 
 

Yeah... I noticed that too. It also makes comfort worse, since it spreads the headband so much there's only a tiny spot on the top of the head that actually touches.
 
Thanks for the picture. Mini XLR seems to fit well in there. I was wondering if it would. This means they can be wired in a balanced fashion, using a 4 pins Mini XLR.

I have the same and thinking of replacing the headband and making this thing bluetooth (or removable bluetooth via the jack). A few questions: What headband did you use? And what did you do to the proprietary jack? Thanks!