Digital clock - any recommendations?

Did not know the Esoteric was multi-box (I know the DCS is; I still see no reason to have an external upsampler).

Still, I believe OP is asking for a reclocker and not actually a master word clock.

I know that Marantz has a clock input, but unless the source also has one, then it cannot be used. Even if so, the internal jitter from the Marantz would still exist.

It would make much more sense to instead buy a $250-$2000 DAC that reclocks internally, and simply use the digital out from the Marantz and plug whatever other sources into the DAC as well, instead of into the Marantz.

Let’s stick with what the OP asks shall we

He wants to use his Marantz SACD player hence an external DAC is a non starter (as there’s no facility to export DSD).

Marantz provide for a 75ohm BNC master world clock input but provide no data on the stability of the internal clock.

It therefore follows that adding an external clock could improve the sound if any of the following apply
1. The external clock is itself more stable than the one in the Marantz
2. The electrical environment in a stand alone clock is more stable than that in the all in one Marantz (btw this is dCS’ argument for a stand alone clock rather than slaving to the one in the Transport)

As even modestly priced clocks as suggested to the OP probably satisfy both 1 and 2 I’d suggest they give it a try,

This review gives a good description of what to listen for when adding a master clock to a one box system
http://highfidelity.pl/@main-815&lang=en

@folkfreak

OP has now stated whether he uses SACD or not, but good point.

I would argue though that regular Audio CD through an SMSL SU-8 or similar would sound be better than even a $10,000 master clock hooked up to that Marantz. Granted, Stereophile measurements show it to be pretty good, except Filter 2.

I do use SACD on occasion.  I am not sure on how such I would spend.  I did see an esoteric external clock for around 4k.  That would probably be the most I would spend.

What are you gonna use the external clock with? Does your preamp/integrated also have a word clock jack? You don’t just plug it into your transport/player. 
 
Or are you talking about a re-clocker? 
 
As I’ve stated on this forum, there is no real technical benefit to DSD in regard to music listening, so I wouldn’t be worried about losing it. 
 
As also discussed, the Esoteric is a multi-box digital system, the clock is used to sync all the components, it is not needed if you are just going analog out from your Marantz to your preamp/integrated.  
  
Room treatment, room correction, and subwoofers would add magnitudes more benefit.