cello, my experience has been that grados have a really hard time with the electronic character of computer based sources. i've never used a g4 as a source but i have tried a variety of soundcards with grados on my pc, including an audigy2, m-audio revo and rme digi 96/8 pst. unfortunately, while upgrading dacs improved things quite a bit, i found all a little bright, not as bad as what you describe, but a little bright just the same. i did not find a significant improvement with ms2s as compared to regular prestige series grados. i haven't tried rs1s or 2s, or any of the older grado designs. if you're determined to use a computer based source, i highly suggest going lossless. to my ears, grados are almost unlistenable with mp3s at any bitrate - they're just too sensitive to the inherent brightness entailed in lossy compression. i've had almost none of these problems when using my admittedly much crappier standalone cdp as a source.