rca or usb digital

Depending on what you are streaming from or using as a server. With my Innuos Statement I use USB to my 680D DAC. No jitter, noise or issues. The only way to connect. 

i have a surrender n20 coming

With an Aurender you are likely to get best performance from the AES connector. This is what I found best from my W20SE. 

Same question, three different answers...that's what i was afraid of. ugh

Whatever sounds better and what the manufacturer of your DAC recommended.

I have a LessLoss R2R with the outboard 640X firewall and 3 inboard. Also use a Innuos Zenith with the Sense software. Zafino Cable USB. No clock as there is no need for it. I also do not use MQA as it a bet of a joke in my opinion. Use Quobuz for streaming and mostly radio..Pardise. .1FM.

Sounds spectacular in my system. Lower grade stuff will require more insularly items to make your digital sound better. DDC, Clocks, ….just my options so take it with a grande and use what sounds best to you.