Oh ok :) As far as I know, I don't know of any "special" tips. I've never really had a big problem with cables failing me and it sounds like you do take care of your gear well so I don't know what to tell you that you don't already know. Maybe someone else has experienced what you are and can offer some insight.
It sound like the sound is coming in and out too often for the problem to be in just the cable, especially since you said you've tried different cables. Check and make sure that your male and female jacks and sockets are good and its not them that are the problem. Try your player with some other headphones and see if anything improves. Check and make sure that your jacks aren't slipping in and out of their socket either. They should "snap" in pretty securely.
It could be wax build up. I have dry waxy ears and it can mess with my hearing on occasion :P If you are looking for an over the ear HP with good isolation, look into Ultrasone. Their isolation is very good and they do have a decentralized driver ("S-Logic Technology") which delivers the same perceived volume but at lower SPL so it's safer to listen to.
Sorry to say but nothing is going to isolate like than an IEM. Having something that fits into your ear canal is going to offer much more isolation than something that sits around or on your ear. I find that my HFi-780s block a good deal of outside noise but they do have a good amount of clamp force.
Take a look at some pelican cases. They have all different sizes that would fit the HE500s plus a DAP and AMP. Plus they have pick n pluck foam which makes custom padding super easy and protective.
This is the one I use.
If you were to choose the "small range speaker" option, I would imagine the software would filter out lower frequencies that couldn't be produced on smaller speakers. When it comes down to it though, I would always have "full range speakers" selected. This prevents the software from making those altercations to the audio stream leaving your computer. You want the full frequency range sent especially to your headphones.
As far as headphones go, the pads get wiped off with an alcohol wipe every once and a while and my iem tips get wiped off when I notice they're dirty but I don't have super oily or waxy ears so this again isn't done very often. My speaker set, up including my receiver (and just around my desk really), gets dusted about every other week or so.