What would be an upgrade over the NAD M51 Direct Digital D/A Converter?

I am looking for some advice as to an upgrade over the NAD M51 DAC.  The objective would be to get my digital end to be more engaging so that there's less of a gap between it and my vinyl front end (Manley Chinook pre, Technics 1200 GAE).  

Would this necessarily require me to spend >$2k?  I'd be fine going used.  I have a Primaluna Dialogue HP integrated, so the replacement DAC doesn't need to have an independent volume control.