[BillK]

I'm currently listening mainly to Google Play Music and CD rips via a Sonos Connect,Lehmann Linear and HD600's. The Lehmann is a new purchase and has taken things to a far better level. I'm now thinking about my next pair of headphones or not. Bearing in mind my source is not up there with the best, would I be best to stick with the 600's (they do sound amazing!) Or is there a lot more to be had going for the 800's or LCD-2's?

 

[Nhubley]

I have heard in one sitting session side by side at my local AV shop the HD700 vs HD600 vs HD800 vs LCD 3 vs LCD 2 all on a Arcam RDAC with a Lehmann Linear Amp.  Here is my personal opinion.  If you like bass and lower frequency Audeze is your can. If you like treble sound stage and over all analytical sound Sennheiser is your man. Boom HD800 one that listen session!
 
If you already have the hd600 I would suggest going with the HD800 if you are going to want to spend the money to hear the difference. Now is there a huge difference. Not really. However, some noticeable difference are the sound stage and the clarity of the HD800 vs HD600.  

 

[KG Jag]

I'm currently listening mainly to Google Play Music and CD rips via a Sonos Connect,Lehmann Linear and HD600's. The Lehmann is a new purchase and has taken things to a far better level. I'm now thinking about my next pair of headphones or not. Bearing in mind my source is not up there with the best, would I be best to stick with the 600's (they do sound amazing!) Or is there a lot more to be had going for the 800's or LCD-2's?

To my ears (and not considering budget) the HD 800 is clear winner between the three.  Between the HD 800 and the LCD-3, it will likely fall to the sound signature your prefer.
 
Check out the excellent analysis of all three cans (plus the LCD-3 and many more) here:
 
http://www.head-fi.org/t/634201/battle-of-the-flagships-58-headphones-compared-update-audeze-lcd-2-revision-2-6-4-13