Streamer output options

I never use usb. Spdif has restrictions on what you can send thru it. If you are paying hires music, say dsd128 or dsd256, you are out of luck. Also, you are restricted to 192/24 files. 
If you are only using a cd player, this wouldn’t matter. I haven’t used a cd player in almost 20 years.

There are some very good low-priced I2S/SPDIF streamers that have extremely good specs, like the Holo Red and the Mercury V3.  I use the Mercury, which is only $500 and far surpasses the USB output of my Mac Mini server in terms of accuracy and cleanliness.  But I don't do extreme upsampling or DSD.

OTOH a friend of mine (who has what I consider a reference system) prefers USB and has a custom-built streamer with JCat USB and network cards.  If he weren't happy with it I would hear about it. ;-)

I think in the end it depends on what level of playback you want and if the higher resolution options are worth it to you.  It seems like you need to spend a bit more to get high-quality USB output, but that shouldn't stop you from going that route.  Relatively affordable USB streamers from SOtM and Sonore are very popular and have good reputations.  Then there's Lumin, Aurender and others that seem to be very satisfactory in terms of USB quality.  At that point, you need to look at the connection interfaces, which vary in ease and quality.  There are a number of threads here about that.

Correct about recent USB. Anyhow we should follow what each DAC manufacturer recommends as best input. 

Agree that it depends on the manufacturer and how they design their equipment.  My Innuos Zen Mk3 streamer has a USB output to my Holo Audio Cyan 2 and it sounds great.  Got it used for under $2K from an excellent local dealer.  I got a short cable that was just the right length from Pine Tree Audio made in good old Massachusetts.  BTW I buy local whenever I can.  Support your local dealers if you can before there’s nothing left but online options.  

I2S was pushed by those selling I2S. Trashing USB was a necessary part of this marketing campaign. I have an Innuos that is optimized for USB. I have a Grimm that is optimized for AES/EBU. I like the AES because it is a great connector and there are a lot of good cables available. However, there are now great cables available for USB.

Bottom line, don’t buy a DAC or a Streamer just for I/O options. Use the option that the OEM recommends as they have implemented that option best.

Beware of I2S as there is no standard for implemetation. So your DAC may do it one way and your streamer another.

Jerry

PS both options have been better than SPDIF in my experience, but SPDIF is better than optical.