Upgrade needed from Sennheiser HD 555's...

Hi all. I bought a set of HD 555's about a year ago. When I first bought them, I enjoyed listening to them very much (I only use my headphones to listen to music). They were my first set of "proper" headphones and I thought they were perfect. The sound was clear, and that's about it. Not so long after, I needed to get some new headphones for my iPhone because my official ones kept breaking so I thought I'd go straight to the top end and bought myself a set of Sennheiser IE8's. I am always listening to music on the go so I thought I'd just go for it! For me, it was one of the best desicions I ever made. The 3 main things that I love about them are the fact that the sound is crystal clear, the bass is very strong, and the soundstage is just incredible. After using them everyday for the past year, I don't enjoy listening to my HD 555's anymore. For me, they sound like the complete opposite of the IE8's and I want to buy a new set of headphones for home use. I would appriciate it if you guys could help me decide which I should buy. I want headphones that sound just as good as, if not better than my IE8's (I want them to be full size cans). The 3 main things that the headphones must have is: 1. Fantastic mid-range. 2. Fantastic bass. 3. Fantastic soundstage. My budget is around £300. I keep pushing myself towards the HD 650's but I'm worried that if I buy them, they might not sound anything like what I was expecting. I'm worried that they may sound too similar to my HD 555's. Please, help me!