Okay, for what it's worth I wanted to post a my impression of a cable swap with the he400. I bought the cable here on the used forum and it was made by Chris_himself. Sorry Chris, I got nothing but love for ya bro'. I want to say that if you are considering an after market cable, Chris makes really really nice stuff at a very reasonable price (shameless plug).
The cable itself:
The first thing that you notice is the size and weight difference between the pure silver over the stock. The silver cables is absolutely feather light. The stock cable seems like a hose pipe compared to it. You don't feel any weight from the cable at all. In a blind test I would not be able to tell if the silver cable or no cable was connected. It's that light. It's finished in a nice double helix 1/4 plug for termination with a nice wooden yoke. The silver cable is also only 74" which means I don't have to run the cable around the back of my desk which I also appreciate. It's the perfect length to run to my amp with about 2 foot to spare for excess. The look is just awesome.
Initial sound Impression:
This is what you'll want to know, right? The silver cable produces a very different sound. It's airy and detailed. Very revealing. I have the velour pads installed currently. The combination of the velours and silver cable reminds me alot of the he500. Don't have them anymore. Compared to the stock cable, the stock has more weight to the sound. Certainly there is more bass extension and impact. I've only had about an hour worth of head time so far after the cable change. Classical is just superb with the silver cable. Pop and rock may be somewhat bass light. Give me a few hours to really audition and I'll post back if anyone is interested.
Heh it'd be interesting if the two cables produce distinctively different sounds, then you could just switch the HE400 'functions' simply by swapping between the two cables.