Hi guys, thanks for the input. Since writing the thread, I have owned Stax 507/323s and Stax 009/Kimik 007tII, alongside Audeze LCD-X and Grado RS1i and various amps like Earmax, Burson Soloist SL and Chord Hugo.
They have all been great, and have provided a very interesting journey through different styles of reproduction.
Right now, I have settled on HD800 as my favourite, fed by the Chord Hugo. My only complaints are that the Hugo isn't great for desktop usability as I like a proper volume control don't like have cables shooting out at both ends. It almost looks like a Raspberry PI or something when it's hooked up.
I'm going to try a Lehmann Linear this week to see how it works with the Hugo and the HD800, but sound wise I think the HD800 and Hugo is excellent.
In terms of the Audeze, I loved the build quality and looks, but found them too smooth and muffled, and simply too heavy and vice-like.
The 507/323s I really liked but the 'Stax fart' from air pressure was too annoying in the end, and the HD800 just pipped them on too many aspects, albeit not by much. They would have been my faves otherwise, and on occasion have been in the lead.
The 009 were interesting, but I found the bass just fluffy and soft, and couldn't justify the outlay when I was trying to decide between these and the 507 combo. I mean, it should be pretty obvious, right! They are super detailed, nice to wear, and tonally brilliant... hard to fault apart from a huge chunk of energiser on the desk, and when you can pick up the Hugo / HD800 and listen anywhere it just wins hands down.
And Grados, well they're fun, easy to wear, look great, really light and a joy to own.However, I just picked up the HD800 every time as I prefer the way they sound and how comfy they are. Shame I look like a Star Wars character wearing them. Still, the HD800 are best headphones i have heard to date though.