Neo is out of my budget - but I'm thinking about balanced WA22 and single WA5-LE. Do the last would be significantly better for the extra costs for HD800? You wrote you have WA5 - how do you feel it with Sennheiser? And how is importante to upgrade to better tubes - or the installed ones are good enough?
I think the WA5 sounds excellent with the HD800, its an honest sound. I think the Sofia Princess 300b tubes are nice, but I would live with the stock for a bit if you take that route.