Materials:
AKG Q701 pads.
Hifiman fitting rings.
Double sided tape.
~30 minutes of your time. 
 
Step 1: Attach double sided tape\foam to the plastic portion underneath the AKG pads.
 

 
Step 2: Attach Hifiman fitting rings onto the double sided tape, squeeze to allow proper adhesion.
 

 
Finished pads.
 

 
Other pads for comparison:
 
Hifiman Velours, Hifiman Pleathers, Homemade Angled Jergpads, Homemade AKG-Hifiman hybrid.
 

 

 
The final result. Make sure to attach the pads with the thickest portion facing the back of your head.
 

 
Impressions with HE-400:
 
Comfort is amazing, the sound is not.
 
Despite supreme comfort, after pumping some bass heavy tracks and playing a bit of COD4 & TF2 I went back to Jergpads. The sound was bass-light, spacious, and airy. These pretty much start sounding closer to AKG Q701 but with shy bass and recessed mids. HE-400 are just one of those headphones where any changes in distance between the ear and the driver lead to drastic changes (usually for the worst). The only reason why one might want to do this mod to their HE-400s aside from comfort is for the sake of gaming, otherwise these are just too bass-light for music.
 
HE-400 is the only Hifiman I've tried this on and wouldn't be surprised if folks with other Hifiman models end up yielding positive results. I'd expect this mod to work out much better on the HE-500 as there are users who have reported great results with the AKG pads.
 
I'm still in search of the ideal comfort pads for HE-400s that don't sound like ass.

Thanks for starting the thread.  I feel really lazy for not having done so after I did the mod.  Shame on me   
 
It'd be fun if other HiFiMAN owners tried this and posted impressions.  I know the only feasible way is to already own the Q701 (or other AKG) cans and pads, but if you can beg, borrow or steal, it might be worth the effort.
 
Of the five different pads I've tried with my HE-500s, the Q701 pads are by far the best for my ears/brain.  YMMV.

Can you get Q701 pads somewhere besides AKG spare parts dept? I got no email reply from them.

soundsgoodtome said:

  Can you get Q701 pads somewhere besides AKG spare parts dept? I got no email reply from them.

Click to expand...

 
Weird.  Maybe you can call.  When I was shopping around for them AKG direct was less than half the price of the only other two places I found them, and only one of those had black (pretty sure it was $35 for one pad before shipping, whereas I paid $35 for the pair shipped).  One site had the gray version which goes with the... K601s?  602s?  701s?  Model escapes me.  Frank Rodriguez's number is posted in a few threads, but I can dig it up, if you need it.  Assuming you'll pay by credit card, you should call anyway.
 
Here's Frank's info:
 
Frank Rodriguez
Customer Service Administrator
AKG /Soundcraft /Studer /Crown Microphone
 
Harman/Microphone/Mixer Division
8500 Balboa Blvd
Dock 15
Northridge, CA 91329
E-mail: frank.rodriguez@harman.com
Phone: 818-920-3279
fax: 818-830-7881

From: Rodriguez, Frank
 
My last day at Harman in March 14th,  All parts inquiries for Soundcraft, AKG, Crown Microphones and Studer will now be handled by David Wheeler and Hector Hernandez.
 
David.Wheeler@harman.com
818-895-3417
 
Hector.hernandez2@harman.com
818-920-3237
 

Click to expand...

 

  If you would like to place an order, please provide the following information via e-mail fax or phone, and I can process the order for you.
 
2458M12020              
$15.74 ea pad
 
Name:
Address:
City:
St:
Zip:
Ph:
CC#:
Exp:
Code:

Harman/Microphone/Mixer Division
8500 Balboa Blvd
Dock 15
Northridge, CA 91329
Phone: 818-920-3279
fax: 818-830-7881

Click to expand...

thurstonx said:

   
Weird.  Maybe you can call.  When I was shopping around for them AKG direct was less than half the price of the only other two places I found them, and only one of those had black (pretty sure it was $35 for one pad before shipping, whereas I paid $35 for the pair shipped).  One site had the gray version which goes with the... K601s?  602s?  701s?  Model escapes me.  Frank Rodriguez's number is posted in a few threads, but I can dig it up, if you need it.  Assuming you'll pay by credit card, you should call anyway.
 
Here's Frank's info:
 
Frank Rodriguez
Customer Service Administrator
AKG /Soundcraft /Studer /Crown Microphone
 
Harman/Microphone/Mixer Division
8500 Balboa Blvd
Dock 15
Northridge, CA 91329
E-mail: frank.rodriguez@harman.com
Phone: 818-920-3279
fax: 818-830-7881

Click to expand...

 Thanks! I'll give him a call. I was also asking about the K712 pads so he's probably just holding those emails off until he has a set date lol

soundsgoodtome said:

 Thanks! I'll give him a call. I was also asking about the K712 pads so he's probably just holding those emails off until he has a set date lol

Click to expand...

 
Guess it's not Frank anymore, so perhaps there's transition confusion 
 
Keep us posted re: those elusive K712 pads.  I do wish I'd thought up this mod before selling my K702 Annie pads.  Curious as to what the HE-500s would sound like with those.  Too expensive to order just to test.

The K712 I found out will be x2 the price of the Q701 however, plus they're not angled so that's a deal breaker. $35 for the Q701 is very reasonable IMO.

I have the HE4 btw. These orthos benefit tremendously from angled pads IMO