I think you would notice a substantial increase in quality, even of your 128 kg/s mp3's, if you bypass the dac on your sound card and use a reasonably priced external DAC. I haven't heard the Blue Circle but it's from a well-regarded company and the strictly utilitarian design of it is appealing. I use a Valab DAC, available for $200 on ebay, between a MacBook Pro and a Nuforce Icon amp and it sounds quite a bit better than going analog from the MacBook to an amp. Even the internal DAC on the Icon is an improvement over the sound card in the laptop with mp3 files.
To Scottlanterman's suggestion about converting your music and using an iPod, you'd have to re-rip everything at higher resolution, not just convert your existing files, assuming you even have the high-res originals. In addition, unless you have a Wadia iPod dock with digital output, you'd be using the DAC and amp inside the iPod and that might not be much of an improvement over what you already have.
To Scottlanterman's suggestion about converting your music and using an iPod, you'd have to re-rip everything at higher resolution, not just convert your existing files, assuming you even have the high-res originals. In addition, unless you have a Wadia iPod dock with digital output, you'd be using the DAC and amp inside the iPod and that might not be much of an improvement over what you already have.