Gapless

Which of the following is gapless playback dependent on?

1. streamer/renderer - assume it is

2. The DAC

3. the digital files. I typically play FLAC files ripped from CDs

I play around with a lot of equipment from about 5-10 years old and gapless might be a moot point now but a short time ago it was not.

My current digital setup is a Krell Connect streamer connected to a Wadia D321 DAC.

I can get gapless with only files connected to the USB jack in the back, but not files fetched with upnp. The Krell is supposed to support gapless playback.

Any thoughts on why the Krell would support gapless via the USB jack but not upnp?

Is it correct to assume that modern (last 3 years) streamers support gapless no problem with ripped FLAC files that are local/USB or via upnp?