The 225 is generally considered the sweet spot in the Grado SR line. That line has the classic Grado house "wall of sound". It's colored and forward. There are many places on the web where you can read about it, but the best method is to put on a Grado SR line can and listen to rock or electric blues.
Do want a portable or desktop amp? In any case stay away from bright amps with the DT 880.
The 600 Ohm version is a step better than the 250 Ohm, but also a step harder to drive. Concerning the 600 Ohm version see:
Since most (if not all) of my listening would be at home, a portable amp would likely not be needed... I did a tiny bit of research and stumbled upon the Objective2. (Open source is always cool) How well would that pair with the DT880s? (particularly the 600Ohm version)
The Grados sound like fun 'phones, but for now at least, I'd prefer to keep to something which would be a bit better all around.
Have not heard the O2 paired with the DT 880 600 Ohm, but know that the O2 will drive them.
You might want to ask how they work together on the DT 880 appreciation thread: