The HD 650, HD 555, and RS2i headphones all sound completely different. So there's no telling what you might or might not like.
I just got the Audeze LCD-2 headphones which is my personal preference. My current headphone setup is now an iMac, Neko Audio D100 Mk2, Donald North Audio Sonett (tube), and now the LCD-2 cans. I'm going to be selling my Sennheiser HD 650 and AKG K 702 headphones soon now that I have the LCD-2.
I just got the Audeze LCD-2 headphones which is my personal preference. My current headphone setup is now an iMac, Neko Audio D100 Mk2, Donald North Audio Sonett (tube), and now the LCD-2 cans. I'm going to be selling my Sennheiser HD 650 and AKG K 702 headphones soon now that I have the LCD-2.