Simply put:
The Grado has a warm "house sound" -Very detailed and sounds the best with strings, etc.(because of the wooden housing. Somewhat agressive, but that can be overcome with flat pads for $30.
The Senns have a darker sound. More nuetral - somewhat veiled detail. That can be overcome by getting the right amp, replacing the cable, etc. Best piano reproduction headphone I've heard. Better soundstage.
