Looking to build a subwoofer. Need Recommendations.

Not entirely sure how different they are, but the XCA series have slightly better noise figures, most likely just different DAC and ADC, possibly different op amps.

The newest ones both have control via network, so that is a major improvement over my unit that is first generation XCA, then the XCA+ came, now it's XCA+ v2.
I am happy with it, value for money, good sound, reliable.
Some more expensive units like Driverack Venu360 have better GUI and functions.