Like the others have said, if you have a chance to get a CD3k, get it, since they are becoming so rare. If you don't like it, or are still curious, try the SA5K, since they are much easier to come by. It's obvious which one I ended up with, but they're both very enjoyable, just different.
Oh, and BTW I didn't find the CD3000 too bright when I owned them, until I put them with the wrong associated gear. I've also found the SA5000 to not sound too bright, but also, with the wrong gear, they have. I think both headphones just need to avoid a bad matching amp/source to aboid sounding too bright.