Importance of clocking

It is helpful to clarify whether the application is using s/pdif or asynchronous USB.

For s/pdif, I think DCS uses what they call "reverse clocking" to minimize jitter in this case an external clock makes sense.  The clock comes from the DAC domain and is used to clock out the transport data.  In this case it is mostly mimic what you  have to the asynchronous USB.

For asynchronous USB the data clocking comes from the DAC domain so an external clock may not help much.  For this, you probably want to have the clock physically as close to the DAC as possible which is the implementation of most USB DAC anyway.

But there is a but.  In asynchronous USB, if the incoming data has a lot of noise, it may inject that noise into the DAC circuit, so you could argue buffering the data with a reclocker will clean up the noise and therefore improving the sound quality.

Andy has a very good point. In the case of SPDIF or AES the clock is embedded in the data stream is more prone to jitter therefore the clock of the source/streamer is critical and IMO could benefit from a good reclocker with a good clock cct and its associated PSU. There are some transports that have a clock input so that the clock from the DAC can be used to clock the data in the transport. As Andy says async USB is supposed to eliminate this issue since the data is clocked by the DAC. Again I agree that a good reclocker/DDC could clean up the USB jitter (noise) but it all depends on the quality of the equipment. The reclocker’s clock needs to be of superior quality to that of the DAC’s one. I believe I2S is the best interface available, it was first designed as an interchip protocol but I see lately is being used to connect sources to DACs. That is fine as long as the interconnects are kept as short as possible.

I had a highly modified Oppo used only as a digital transport (all audio/dac board removed e.t.c). One of the mods was an upgraded clock - but not just that - a unique dedicated linear power supply just for the clock alone. This hugely lifted the performance of the transport. I was running it spdif out to an external DAC.

Interestingly the clock was a SAW (Surface Acoustic Wave) clock, not an TCXO or OCXO. The people behind this mod were adamant that SAW clocks were superior in sound quality to OCXO clocks. I have never seen anyone else in the high end audio industry even say they have tried SAW clocks.

Unfortunately the Oppo mainboard itself died and all those mods (like a full on R-core LPS powering the mainboard) turned it into a paperweight. It was a way better sounding transport than any entry or medium level product you can get now.

Spend your money on a good DAC that includes a good clock.  Spending thousands on a clock is a huge waste of money, IMHO.  

As mentioned earlier, the main purpose of an external clock is to synchronize multiple devices, not to improve sound quality. 

If there is an improvement in sound quality, it's going to be much less than you could have realized by putting your money into a great DAC.  Lipstick on a pig and all that...

The issue with S/PDIF or AES "reclockers" is that you have two clocks arguing over what should the absolute clock rate be.

The DAC is forced to take one of two approaches: Abandon it’s internal clock or attempt to keep it’s internal metronome and "fix" upstream deviations from it’s own mechanism. This is exactly the thing pro clocks do, but only because there are upstream devices manipulating the data stream. They are there to stop an inevitable argument that arises as a result of a studio’s workflow. Home users HAVE no such arguments to solve, but can create them by adding upstream clocks.

Maybe the best of these situations is to use an Asynchronous Sample Rate Converter, like in the Schiits, but then you’ve got to deal with the fact that your DAC is no longer being given bit-perfect conversions.

In measurements done, I’ve seen original DAC jitter perform actually get degraded, and the signal looks like the upstream jitter PLUS the DAC’s original jitter signature.

Either use an integrated streamer/DAC or a streamer with a multi-second buffer plus USB / asynchronous communication with the DAC is the way to go IMHO.

I should point out, use whatever you want to which sounds good to you, but so far all I'm reading is a misunderstanding of how and why studio clocks work.  I'm going to go with the documentation from Benchmark and Mytek and say it's a bad idea.