To DDC or not to DDC. That is the question.

Your Merason DAC 1 uses the Amanero Combo 384 USB module, which is considered a high-level, audiophile-grade, asynchronous USB interface that is highly regarded in the high-end audio industry, and is commonly used as a premium OEM component in high-end DACs for its exceptional jitter performance and support for high-resolution formats. Therefore, from a sound quality standpoint, as long as your digital front-end server/streamer has a good quality USB output, there would be no reason to add a DDC, which would result in your needing to switch to the AES or S/PDIF input.  The only reason I can think of for you to consider using another input (other than USB) would be that the AES input might sound slightly more dynamic.

I respectfully disagree with this.  Feed ANY DAC a a cleaner signal whether it’s galvanically isolated, buffered/cached, well clocked, whatever, and it will perform better.  Many people here have experienced this.  Bottom line, you won’t know if a DDC makes an improvement or not until you try it.  Might not, but more often than not people who’ve added a DDC have experienced material improvements, hence my recommendation to just try one used or on demo cause you really can’t know until you try.  The rest is just theory and supposition. 

@soix 

hence my recommendation to just try one used or on demo cause you really can’t know until you try.

Exactly right.

But @maprik and others should know that, just like all other audio gear, different DDCs will change your sound quality to different degrees.

Most will probably improve your sound quality.  A few will probably degrade your sound quality in one or respect or another, or might make a change that is subtle, and not worth the expense.

So if one DDC does not please your ears, then a different one will.  As @soix wrote:

Many people here have experienced this.

Do not let a possible first attempt, that might not work out, sour your taste for a good DDC.

By the way, the Singxer SU-2 and SU-6 DDCs get high praise, at a fraction of the cost of the Berkely Audio Design re-clockers.  The SU-6 is the higher model.  I do not know why there is no SU-3, SU-4, or SU-5.  They seemed to jump from SU-2 to SU-6.

@soix - I am not sure which part of what I wrote you disagree with.  I own basically the same DAC as the OP (except the upgraded version) and I also own a pretty good (super low jitter output) DDC (link) that I have used with that DAC over an extended period.  The USB input compared to the AES or S/PDIF inputs is apples to oranges.  The USB input is asynchronous and performs mainly on the strength of the DAC's USB input.  The AES and S/PDIF inputs are synchronous and rely more on the source clock and the quality of the signal provided.  The main other factor is how good the streamer is and whether it is optimized for a high quality USB output.  I have two very good streamers here now that are both optimized for their USB output.  IMO, the DDC does nothing to improve the sound of the Merason DAC in my system.  The USB input of the Merason DACs is highly optimized and well respected (better than most).  Therefore, if the streamer being used outputs a quiet and well-clocked USB signal, my experience with virtually the same DAC is that, to my ears, the USB input sounds better than either of the others coming out of a well-respected DDC.  That is the basis of my suggestion to put the money into upgrading the DAC.  The Mearson DAC upgrades are well-regarded and reported to move the ball forward wrt sound quality by the owners who have had them performed.

All that said, even in my system, the sound between the two options is a pretty close thing and I could envision an owner who would prefer the sound through a DDC and the AES input.  I find the USB input provides a little more body, musicality, and fluidity while the DDC into AES or S/PDIF inputs sound maybe a little more muscular. If I were on a budget, I would upgrade the DAC first and then I could always try different DDCs later.

You are correct that there are too many variables and that listening in one's own system is the only way to be sure of what a listener enjoys the most.  Not everyone here can afford to try all the permutations and so they reach out for advice and suggestions.  It is not unusual to get different suggestions from different posters. Just ask which USB cable sounds best ...

There are a lot of variables and the only way to find out how it will play out in your system is to try for yourself. Some of these DDC units are excellent for a pretty reasonable price, so there's low risk involved. Either buy from someplace with a good return policy or else pick up a second hand unit, and flip it if you don't end up hearing an improvement.

I like the Denafrips units and their Musician Audio counterparts, all very well built, great connectivity, and of course superb sound. 

I checked out the Merason upgrade to Mk2 and Im not sure if I want to lose the musical analog quality that the Mk1 is known for. If only someone in my area had a Mk2 I could listen to in my system. At $2400 for the upgrade I'm leaning towards testing out a DDC in the $1200 range that I can flip if I decide its not an improvement... or I could buy a bunch of records.... the dilemma of having a monthly audio stipend!!