The ONLY difference between the T51p and T51i is the inline iDevice controller/mic. They are the same headphones otherwise. And fellas, when run out of my iPhone 6 or iPad Air, the soundstaging is on the "narrow" side, but on my AK100II, you'd be surprised how much this improves.
Here are some of my favourite rock albums from the 1980s (when I was in high school):
1.) Van Halen - 1984
2.) Def Leppard - Hysteria
3.) Bruce Springsteen - Born in the USA
4.) U2 - Joshua Tree
5.) Black Sabbath - Heaven and Hell
6.) Jeff Healey - See the Light
7.) Dire Straits - Brothers in Arms
8.) Metallica - The Black Album
9.) Pink Floyd - The Final Cut
10.) AC/DC - Back in Black
I've owned both the WA22 and GS-X Mk2 (still own BTW). My WA22 was tricked out with some really stellar NOS tubes and the GS-X Mk2 was the better amp by a long shot to my ears. Might explain why it's no longer with me and the GS-X Mk2 is still here.