I'm surprised that there's no SPDIF input, but if market research suggest that USB is the dominant carrier method these days, I'll accept that.
Perhaps Meridian's market researchers should have looked at Meridian's own components, none of which, to my knowledge, has a USB output. Yes, they have analog outputs, but I think my G91A converts all inputs to digital. I hope I'm wrong about this, because otherwise listening to an SACD through the Prime would involve two A/D conversion stages.
I'd be curious to know how many other DAC/headphone amps in this price range lack an SPDIF input.
Just to prove I'm able to see the glass as half full, it's good to see the Prime will power balanced headphones, although it wasn't clear to me that the Prime was itself internally balanced.