DAC suggestion Please

Going up to LS50 actives would be a much better upgrade path, IMO.

I would say that upgrading either the active speakers OR the DAC will give an increase in sound quality.  The KRK Rockit are not bad, and they are at the same level as my Yamaha HS8 (only smaller).  I have been able to make my Yamaha monitors just "sing" by doing DAC/preamp upgrades as well as power cord/fuse upgrades.   Sure, the Kef LS50 are definitely more accurate and high resolution, but the DAC source is important as well.

Thanks for assistance.
End Result
i bought a Chord Qutest for my "big" rig

I upgraded the speakers on my "desk rig" to Fluid Fx8 and am moving the Chord 2Qute to desk.  

@saleh84 Why do you think R2R DAC sound better compared to sigma delta.

Former ZDAC v1 user here. Spring for a used NAD M51 for your price range. Should be able to pick one up for around $750 shipped. You will not be disappointed.