In the past I have owned a few Sennheisers (HD555, 580, and 600) and heard an HD650 and HD800 and a few Grados (SR80, 125, 325, PS500 with stock pads, and a PS500 with really big pads, not sure what model) at a meet.
I'm not a huge fan of most Sennheiser headphones, but the HD650 and 800 are great. I wasn't a fan of the Grados I heard at all due to their lack of bass and terrible comfort factor. The PS500 with the bigger pads wasn't as bad in the comfort area, but that material is still too rigid for ear pads IMO. I didn't like the extremely bright factor to the Grado sound, extremely fatiguing to my ears.
Now, for the SG. I have never heard the stock PX100 so I can't compare it's sound to the SG to hear where the makers/contributors may have improved the sound. When I first put them on it felt just like a Grado (surprise!), but when I connected it to my Aune T1 and started the music is when I found the difference between these and Grados. The sound coming out of these is much more voluptuous and thick than any Grado I've heard, like fruit smoothie thickness compared to the Grado's water-like sound.
There is a pretty nice low end to these, they gave my metal music a heavy sound, I could really enjoy a nice drop while still hearing the vocalist, guitars, and cymbals very clearly and totally separated from one another. You would never think to use a Grado to listen to Dubstep, but these held up to the task fairly well. They have nice impact but the sub bass is lacking (a pad swap would probably counter this). These are more mid-centric than anything, vocals are right up front, the bass is right below that and then the highs behind that. If I were to compare these to any headphone I have owned, I'd say they're closest to the Audio Technica ESW9 with less bass and impact but a larger sound stage.
I did do some gaming with these on. I played Battlefield 4 on Xbox ONE with these connected to my Astro MixAmp Pro. The staging is fairly good, you might think an enemy is farther away than they actually are. Gunshots from your own gun are extremely in your face, but I suppose they would be if you were firing in real life as well. Overall they handled gaming well. If you only wanted to own one headphone and preferred these for how they perform with music, they would do you just fine when you were gaming as well.
Overall these are great headphones to the right people. I'd say if you were considering buying a PS500 for how they handle music analytically, you'd be doing yourself an injustice by buying those over these.
