My system with subwoofer uses RME ADI-2 DAC FS while my wife uses a Rode AI-1 that is an audio interface. Earlier I used a Motu M2 as DAC for and headphone amp, and when I bought the ADI-2 the M2 was then only used for mic duties. Now the M2 is replaced for mic duties with a RME UCX II for the features and connectivity it has over the M2.
The major difference among the DACs in sound quality comes down to features and DSP in that I use the Dynamic Loudness feature of the ADI-2, which I like very much. The bass/treble tone controls are handy as well on occasion. I don't use PEQ for the monitors as they are calibrated but I use them on my headphones.
The GLM Kit makes a huge improvement in sound quality when used for room calibration as well as integrating the subwoofer. The kit is around 350 Euro and is very much worth the money.