ARE SUPER EXPENSIVE STREAMERS REALLY WORTH IT

Whatever interface one uses they all can be less or more depending on one's optimization. While I2S has some inherent advantages that doesn't mean it will always sound better than usb  or whatever. Clocking and power supplies to the clocks is of utmost importance.. Three categories of clocks, femto, txco, oxco, in theory the order of quality least to most is femto, txco, oxco. In reality a well implemented femto clock could outperform a less well implemented oxco clock. The quality of the clock itself and more importantly the quality of the power supply to that clock matters a lot.

The above holds true whether comparing I2S implementations or comparing usb vs I2S implementations. The most optimal implementation for either of these interfaces would be a well implemented oxco clock in both streamer and dac. Good luck trying to find that in either streamers or dacs. space limitations for the power supply alone make it very difficult to implement. Femto clocks are easiest to implement with these space limitations, cost considerations probably play a role as well.

So, wide variability in clocks and interfaces and we haven't even gotten to differences in motherboards, processors, RAM, operating systems, linear power supplies, music player apps. All have a bearing on sound quality.

And then we haven't even gotten to differences in optical vs ethernet, switches vs routers, digital cables, modems, linear power supplies to all these devices, and I may be forgetting some things.

Some believe you can just slap in any streamer and get the same quality of sound with a fully optimized streaming setup. I and many others have experienced otherwise so believe whatever you want to believe.

From Antipodes: 

"a clock stage is only as good as the circuit it is used in and the power supply that powers the circuit. And the re-clocking stage needs to receive a low-noise signal with high-bandwidth, before it can re-clock the signal accurately. If the signals before and after the re-clocking stage are polluted by noise below the bit-rate (such as from employing linear power supplies) then the re-clocking will be largely ineffective. Anyone that claims that digital is 'just ones and zeroes' has not applied their knowledge to demanding real-world problems."

All the best super-expensive, no compromise streamers have gone to huge lengths to develop their power supplies, which is a large portion of their expense. 

@russbutton  I’d encourage you to at least demo a decent streamer from a place like Crutchfield, Amazon, etc. that allows for returns rather than blindly holding on to the belief that it’s all just ones and zeros.  Hundreds of us here have found that’s absolutely not the case for audio — not even close, so unless we’re all somehow wrong and fooling ourselves it’d be worth your while to at least try. 

there is a reason why people buy a $7000 Sean Jacobs power supply for their Chord Dave.

Yep

To the OP:  Your emphasis on the clock is a mistake, imho.  The impact on sound from a quality clock/reclocking is easily measured (jitter).  The only source I know of that consistently measures jitter in streamers is HiFi News.  So I put together a small database of 13 streamers measured by HiFi News over the last few years; the two streamers costing £1k or less have jitter levels at about the same levels as the 11 higher cost streamers (up to £33k), and these are vanishingly low levels of jitter.

So that leaves only one other area of potential difference among streamers:  power supply-related noise.  And as some others have mentioned, DACs vary widely with respect to their sensitivity to noise; some are largely immune.  Unfortunately, HiFi News measurements of this - thru signal-to-noise ratios - is less comprehensive.  However, what measurements they have done on this issue suggest, again, that you don’t need to spend a lot of coin on a streamer.  There are well-engineered noise-free streamers available for £1k or less.

Finally, my own experience of streamers over the last 20 years, including a fair number of direct A/B comparisons, has confirmed what the data show.  Isn’t it great when the science and our experience are consistent?

I have now shortlisted some streaming products from Aurender and Lumin, maybe I might add HI FI Rose also. I am still looking at options for DAC’s that maybe a possible synergistic match for these products as well as the rest of my system.

Cool! Plenty of choices out there. The two you have are two of the most popular in this forum. In addition to names I gave above, add Innuos, EMM Labs, PS Audio, Melco, Moon, Audiolab, Auralic, Wattson, Cambridge Audio, Cyrus, nobody here ever talks about Naim, rarely Linn- who invented the high end streamer. I guess it all starts with budget. 

Here is one cool "network player" that is totally upgradeable and customizable- buy the modules you want and don't pay for ones you don't- check out the review: 

Aqua Linq