Bitrate has nothing to do with the song's recording. If the song was recorded or mastered poorly to begin with, a higher bitrate will only make the flaws in the song more apparent.
I gave super girl a quick run-through. While I've heard worse, the recording definitely is a bit shrill and bright, and also a bit compressed sounding overall. A lot of higher end headphones have liberal treble spikes to give everything the illusion of more detail and a crystalline attack to make them seem more crisp-- beyers are a good example of this. It will make lots of recordings sound real good, but it will make the wrong recordings sound really bad.
I've compared supergirl between my iMac's onboard (intel hd audio-- not half bad) and running through my HRT Music Streamer II and Little Dot MKII with Mullard Driver Tubes, and the dedicated dac/amp definitely make the shrill recording less apparent and the sibilance becomes more tamed-- it's overall more smooth and warm.
Try a warm recording like Corinne Bailey Rae's Like a Star, and see if you're getting as much sibilance issues. Also note that a lot of times when you push a lesser amp, it will cause unwanted treble spikes in the sound, so you might be experiencing some of that as well. Regardless, you may want to consider a dac and tube amp, a warm solid state amp, or a headphone with deliberately rolled off treble, like one from Sennheiser.
Edited by TMRaven - 8/30/11 at 9:01am