Roon-DSP: USB or Ethernet?

[BlackJack]

Please read the following thread where all has already been said:

What can/does a Roon Nucleus Do and how do I play through Roon in another room?

I have enjoyed Roon for many years in a very simple system (Nucleus → Novafidelity X45 → Meridian M20 active speakers). However, it appears that Novafidelity/Cocktail audio has folded in UK, my X45 has stopped receiving any firmware updates and will probably soon be obsolete/incompatible. I have been thinking about replacing it and recently consulted a respected local HiFi retailer. He showed me various expensive alternative streamers/preamps/DACs in various combinations. I asked why I could…