First, things you're going to need. (NOTE: Everything I did here can be done with parts found at Radioshack. They even sell SOL REPUBLIC replacement cables (Limited selection though)).
1. Your SJ55's! What? Did you think you could do this mod without headphones?
2. A SOL REPUBLIC cable of your choice. (They come in different colors and designs. I recommend buying them straight off the website*).
3. A small screwdriver.
4. A soldering iron and solder (obviously).
5. (Possibly) A dremel.
6. Some sturdy glue. (I used super glue, loctite and hot glue)
7. Two 2.5mm (Yes, they are 2.5mm, not 3.5mm) female phone jacks (mono or stereo will work for this).
8. A steady hand.
Now, how to build these bad boys.
1. Remove cushions (they come straight off, nothing special here), and remove the four screws holding the drivers in place.
2. This is do or die: Cut the wires and remove the drivers. This is the point of no return. You are a true DIY-er. Good luck!
3. You'll probably have these rubber things in the drivers still. Get some needle-nose pliers (or even some tweezers may work), and pull them into the headphone. This is where your jacks will go. Luckily, Audio Technica have made this mod easier, courtesy of making these holes just the right size for 2.5mm jacks already!
4. If you've gotten this far, you're committed. You are a true student of DIY. Give yourself a round of applause! Now, back to work! There's this plastic thing that may, or may not be preventing your jack from fitting correctly. If it's a problem (as it was for me), then you're gonna have to break out the dremel and sand away. Be sure to blow/wipe any plastic dust off the housing. This is where your steady hand will pay off. Good luck.
5. Now we're getting somewhere! Time to break out the soldering iron and solder the connections on! You may find it helpful to use a bit of hot glue to reinforce your connection (like I did). (Fun fact: As for wire color, copper is common/ground. Any other color is for signal) (Fun fact 2: SOL REPUBLIC cables use stereo jacks that carry a mono signal, so as long as you get ground right, there is no way you can mess this up!).
6. Glue them in place. Do this well, you don't want to end up with the jacks falling inside of your phones. I used super glue for adhesive, and hot glue to prevent rattling.
7. THIS IS FREAKIN IMPORTANT! LEARN FROM MY MISTAKES! Okay? Okay. Don't put them together yet. I recommend leaving them overnight open like this to allow the glue to cure completely. I ended up with super glue on my headphone jack connections which was a pain to clean up when they were back together. You can survive one night, right?
8. Test 'em out, and put those heaven-sent, one-of-a-kind cans back together! At long last, your creation is complete! Looks like the work of a masta (sorry, Wu-Tang reference)!
Wait, wait. I can already hear you clicking away at your keyboard asking about audio quality before and after. Look, to me, they sounded slightly better after this mod. But to be honest, it's probably just me. And until I have another normal pair to compare them to, I'll never really know. But I have techno-blue cables now, so I don't care. The satisfaction of DIYing this mod made them more enjoyable for me, maybe they will for you. Good luck!
Edited by FRESHPINETRICKZ - 4/12/14 at 8:28am