I'd say in terms of SQ the sweetspot is between £1k and £2k - I think you pay more for features such as smarter more flexible interfacing, additional features and even looks - which may or may not be relevant for you.
I think there is a lot happening with DAC reconstruction filter technology at the moment - not least because of significantly more powerful extremely low heat/electrical power signal processors as used by the DAC reconstruction filtering process - this is allowing the boundaries to be really pushed and many of the established practical compromise norms in this area over the last 30 years or so can now be cost effectively challenged and improved upon.
Therefore I would not pay significant above the sweetspot on a DAC unless you are quite happy say for in 5 years that premium high class DAC could be an also-ran and be superseded by newer approaches and technology. I contrast this with analogue electronics where designs from twenty years ago are still current and market leading all these years later.
