I just made myself a 4P -> 4S converter cable, and it was indeed very simple to make. I used 80 ohm vishay dale 1/8W resistors, gold plated stress relief miniplugs (not sure of the brand) and some stock cord from an old 70s style coiled headphone extension cable.
The only (relatively) significant cost I incurred were the miniplugs, which were 6 bucks for both. The resistors are under a buck. I could imagine the cord adding some cost, depending on what you choose, but so long as you don't go above $5/foot (which in my opinion is WAY excessive given that you're plugging them into your stock ety cable anyway) you will come out ahead. The soldering is simple and my cable works beautifully.
As far as the bass question goes, I would say that it is a bit reduced while i'm walking around. In fact, it is not so much that bass is reduced, as it is that internal sounds (walking, breathing, chewing, blood pumping, etc.) generate a lot of low bass background in my ears. The isolation is fantastic, but it also results in *internal* sounds staying inside my ear. Hence I can hear myself breathe, when I'm walking I can hear my heels hitting the pavement, and I can hear my heartbeat and blood rushing in my ears if I sit quietly. These low vibratory sounds are in the bass range, so they can obscure the music's bass.
On the flip side, I should say that the benefits of the sound isolation far outweigh the negatives. Several others have expostulated on those benefits ad nauseum so I'll let you read those threads.
Isolation aside, the sound is better than anything I've ever heard before (or since). The bass is different from over-ear headphones because it doesn't vibrate your head...it is a pure signal felt only at the eardrum, which takes some getting used to. Having heard it, I will never go back.
Hope this helps!
