Hi ProtegeManiac,
It's not that I need them so much, more that I'd enjoy collecting and owning them and using them depending on my mood. I love the HD650s and when I bought them I thought it would hard to beat them by any large stretch, then I bought the 800s and I realised that in many ways that wasn’t true and they are amazing. But they each have their character, the 650s are great for some more shameless listening, something rocky for example, because of their bass signature and less challenging detail. I do love the 800s, they are an amazing pair of headphones and currently I’m using them more than the 650s.
The 800s have a wonderful clarity that makes listening to them a joy, however they are exceptionally clear and revealing. I’d use the 800s if I want to really get into thinking about the music and hearing every detail, I find this wonderful but it does take more focus and distracts from a simpler level of enjoyment. If I just want to switch off and take some time away from life the 650s are awesome for that, they don't take the effort the 800s do and that can be exactly what I'm looking for at times.
I think the 700s should fall somewhere in between those, allowing me a little of both if I don't want to completely switch off, but also allowing enough clarity to get inside the music and appreciate it technically when I want too, but not to the same extent that the 800s do.
That was the rational justification, the irrational side of this is my love of completing a collection (can be anything, if I enjoy something I can get a bit collect obsessed). If I bought the 600s and the 598s, etc, this would only be for the last irrational reason. But I still may do that.
All this aside, the HDVD800 has 4 headphone outputs so if some friends come around we could all try them out together and demo them, assuming they want to check out the headphones.
I hope that makes sense.
Dan.