36,
I would recommend some sort of amp with the X1s if running straight from a laptop (though I do not know what kind of sound card you have). I have a typical Asus laptop - nothing special - and and the sound, for want of a better word, sucks; not just on the X1s, but headphones/IEMs in general. I have had great success with the HRT Microstreamer, but something as inexpensive as the NuForce uDac is pretty darn good. If you don't need a DAC, any one of Fiio's portable amps should work nicely - you'll find the X1s do like some juice.
As far as the cable goes, I believe the issue has been blown out of proportion. When I ordered mine, I bought the obligatory low impedance cable (V-Moda) because I thought that was what I was supposed to do. There may be a small tightening of bass, a clearing in the highs, but no "wonders" or "night and day" differences. It depends on the source as well. I notice a larger difference (albeit still very slight) from my HRT than from the headphone out on my integrated amp (that thing is a monster!). I signed up for a "cable tour" one of our generous members put together and am curious to see of my ears are golden enough to tell the difference between the OFC and SPC cables coming soon.
As far as genres go, I have been having a blast throwing everything I have at them and have found no deficiencies. They make everything sound fun and that is exactly what I am looking for. "Neutral" and "analytical" are not my pursuit at this time. I was a "head on chin" audiophile for many years and have since quit obsessing over equipment - now it I listen simply for the sheer joy of it, which the X1s deliver in spades.