Thanks for the recommendations.
The Little Dot looks interesting, but if the budget is upped a little the Schiit Valhalla comes into range.
I have always fancied a piece of Schiit.

An OTL headphone amp? Is it a good idea.
Maybe I should speak to Mr Fitkrebottle and see if he can make me one with a massive power supply. As apparently they make all the difference.