Left filters stock. I'll give EXACT clock mode a good try (wasn't sure it would work.) I'll have this DAC in my house for a few days to give it a good run.
The stock (default) Filter 4 supposed to be a good all around and based on AURALiC tests collected the most positive feedback during subjective listening testing, but it's not the most detailed.
Filter 3 is the warmest with strongest treble cut off. And No 1 the best measured, try that one if you want to extract more "plankton", this and EXACT clock would squeeze out the most details. Also covering pin 1 and 4 on USB connector seems to help too.
Also check out this document, it provides thorough explanation on Vega filters