Headphone Distortion?

Having long ago sold my great playback system, I decided to again dip my toe into the audiophile pool, & purchased a nice used set of Grado gs1000i headphones and a Marantz SA8004 cd player, with the hope that I'd be OK without a headphone amp or a better cd player. Usually I hear beautiful music, but often on bright instrumental passages or loud brass or high pitched instruments, it can sound distorted and smeared...not at all musical. I wonder if it is the recordings or characteristic of my equipment. Certainly not playing loud enough to distort. Any thoughts or suggestions to tell if my equipment is damaged or if the CD player is not up to the task will be appreciated.
You probably need to get a headphone amp. Have a look at this website. headphone.com. Its a very good resource for anything headphones.
Even a modest headphone amp can make a difference. I have a pair of Sennheiser 600 phones and AKG701Q's. They both sound so much better through the single tube Bravo Ocean amp (120 bucks new). You can get better amps in the 250-400 range. I strongly recommend tube or tube hybrid.
I use a Marantz SA 8004 as my source...I've never heard a review comment about such distortion. I suspect my headphones are very "sensitive" to input. I may try replacing the cables first and see if that cures it. If not, then a headphone amp. I've read several reviews of some of the popular moderate priced head phone amps (<$500) and reviewers feel that the 8004's playback is at least equal if not superior. Unfortunately, I do not have the luxury of auditioning my equipment locally.
Check out reviews and discussions and head-fi.org

Not as solid and reliable as audiogon, IMO, but if you look you can find people with good ears and discriminating taste.
The problem is that your Marantz unit has a headphone output that is probably an op amp worth about 5.00 if that. If you can find a junction box to take advantage of the real Marantz sound...you will hear a world of difference. OK...or you can get a dedicated headphone amp.

Since I have a Marantz 8004, it was no problem for me to go and listen through Ultrasone HFI- 700 Headphones, and they sounded beautiful; the CD player is up to the task. I suggest you continue swapping out until you find the source of your problem.
I have the Grado 1000s and I don't think they're really made to play very loudly. I mean, they'll play louder than I want to listen, but they're not for headbangers. I've never heard mine distort like you're saying, so maybe you need to try them through another source to see if the same thing happens. I use that little Audioengine USB DAC with my computer and they sound great.