.
It seems that the MR816csx interfaces do have a sample rate converter on both digital inputs.
I tested this with both MR816csx SPDIF coaxial input and optical input.
I did not see this feature described in the manual neither in the advanced manual so i’m surprised to discover that.
So, here is how i did discover it :
I was working on a 88.2 KHz Nuendo project, and i needed to listen for the optical SPDIF input. On this input there was a 48 KHz source, running asynchronously from the 88.2 KHz MR816csx clock.
The MR816csx clocking was set on Internal.
I did switch the Nuendo control room monitoring to the Ext input that was assigned to this optical input and to my surprise, i got audio without any clicks. input signal at 48 KHz sample rate was converted to the 88.2 KHz internal sample rate.
The MR816csx did not switch to 48 KHz to accept that 48 KHz digital input because i was able to listen to the mix (88.2 KHz) at the same time. This mean that the MR816csx was running at 88.2 KHz. And the 88.2 KHz LED was still lit on the MR816csx.
I did create an audio track with the 48 KHz Ext input on it with monitor button enabled to check that both the mix (88.2 KHz) and the optical input (48 KHz) were running without problem and were mixed together. Both the mix and the digital input were running and mixed together flawlessly.
So this prove that there is a sample rate converter inside the MR816csx 
I did go a bit deeper and tried to connect another source at 44.1 KHz now on the coaxial SPDIF input. This time this was not working. But :
When disconnecting the 48 KHz source on the optical input, then the 44.1 KHz coaxial source did play perfectly !
In fact, to get a digital input working, we need to disconnect the other one, if both have different sample rate frequencies.
This mean that there is a sample rate converter on both inputs, but that it cannot convert at the same time on both inputs when both sources have different frequencies.
Now the most interesting part :
Both digital input sources can run asynchronously from the MR816csx internal clock, if they are both at the same sample rate !
And it seems that both digital input sources do not need to run synchronously.
For example :
Still using the 88.2 KHz Nuendo project, MR816csx at 88.2 KHz internal clock, i did connect two 48 KHz sources on both SPDIF coaxial and optical digital inputs, both sources were running at 48 KHz but asynchronously.
And surprise again, both sources were converted to the 88.2 KHz MR816csx internal clock without any problem !!
Conclusion :
The MR816csx do have a sample rate converter (SRC) on both SPDIF inputs (coaxial and optical) but it does have a small (or big according to what you need) limitation : it cannot convert both inputs simultaneously if they have a different sample rate.
But it can convert both inputs at the same time, if they have the same sample rate, different from the project sample rate, even if each one input is running asynchronously from the other one.
This is a quite interesting SRC configuration, not a true independent asynchronous SRC on each input, but still interesting for most uses because it does allow to convert two digital asynchronous sources at the same time. The only restriction is that they need to have the same sample rate. For example both at 48 KHz or both at 44.1 KHz, and the Nuendo project at 88.2 or 96 KHz.
This is only preliminary tests. They would need a more serious distortion analysis to quantify the conversion quality.
Anyone did notify those SRCs too ?
I would be curious to know if the UR824 do have them too.
.