Jim is right.
Both the RCD 510 and RNS 510 sound utterly awful on their own without the help of Dynaudio (which Gizzy has) or a separate amplifier.
I have said this many times and wish it can be accepted as gospel.
These units on their own sound CRAP.

Additionally, even with Dynaudio or separate amplification, a sub-woofer is mandatory.
Question: Why do you think VW offer Dynaudio with the RNS/RCD 510 units and not with the RCD 310?
Answer: Because VW know that they sound rubbish without Dynaudio.
QED. 