Does removing "interface jitter" help, if my source has jitter?

I'm thinking of getting a Benchmark 3 DAC, and one of the selling features is its UltraLock3™ jitter attenuation system, which Benchmark says "fully isolates the inputs from INTERFACE jitter" (emphasis mine).   If my upstream source has jitter, will this system isolate that from the DAC?  My usual source is a Blusound Vault, and I suspect its jitter control is not as good as the Benchmark's. 
Yes it will. It buffers the signal and uses it's own clock if there is any jitter it's not perceptible. 
Having good jitter reduction and a good clock internally always helps. :)

Best of course is to use asynch USB so the clocks short and long term match up perfectly.

To be honest though, around 2010 or so DAC's jitter reduction seems to have improved remarkably. It's really hard to find a DAC that doesn't have absolutely excellent jitter rejection at any price.
Any jitter on S/Pdif will be suppressed.  It doesn't matter what introduced this jitter (CDP or digital cable).  The only jitter that cannot be removed is recorded jitter.  Early digital recordings were sometimes done with poor, jittery A/D clock.  Such jitter cannot be removed and the only way to fix it is to digitize again, if analog tapes are still available.
Any jitter on S/Pdif will be suppressed. It doesn’t matter what introduced this jitter (CDP or digital cable).

It’s unanimous! Almost unheard-of on Agon.
Little too quick on the trigger there sunshine

If this were correct there would be no difference to be heard (and there is I’ve heard it ) if a separate word clock cable was used to sync both transport and dac off the one "dac clock", instead of them using their own clocks.

Cheers George
The Benchmark DAC 3 distortion and noise level  is -140db no need to worry about jitter induced distortion.  This is true of competently engineered modern DACs. There are even a few R2R DACs that manage to keep distortion and noise below human audibly but I wouldn't waste money on them they're overpriced. The RME ADI 2 FS is very good DAC that's cheaper than the Benchmark. 
Benchmark does not recover clock from the data.  It ignores it (asynchronous rate converter).  Benchmark specifies insane jitter tolerance of 12.75 UI bellow 3kHz and 1.5 UI above it.  At audible frequency of 10kHz jitter tolerance would be 0.1ms * 1.5 UI = 0.15ms.  That is still insane amount of jitter (0.15us typical jitter will be more likely).  Benchmark defines tolerance as "With no measurable change in performance". Perhaps we can hear what is "no measurable" but we're talking 1000x difference between typical jitter and Benchmark's tolerance.
I knew I could count on you, George…(it’s been a loooooooong time since I’ve been called sunshine).
I knew I could count on you, George…(it’s been a loooooooong time since I’ve been called sunshine).

Well you were applauding and doing cartwheels like an excitable school girl, after only 12hrs and 3 posts of starting the thread up and asking the question..

Cheers George
@yyzsantabarbara Thanks for sending a link to the Gustard review; it sounds like a very impressive unit.  Do you know anyone who has heard it?
@cheeg I will hear it myself on Thursday. I bought it a few days ago and it is being shipped from China. It will need some time to burn-in.

I have a 30 day trial period with this purchase.
@yyzsantabarbara That's great! Mind if I DM you next week to get your impressions?
@cheeg No problem. My frame of reference is the AudioMirror Tubadour III SE tube DAC that is really growing on me. At the other end is the Benchmark DAC3B that is amazing on great recordings and a little strong on bad recordings. I am hoping the Gustard is just right in the middle of those 2.

I was hoping to use the CODA 07x preamp with the Gustard and RAAL SR1a but the preamp is delayed another 2 weeks. So I will be focusing the Gustard on my floor standers with Benchmark gear (HPA4 + AHB2).
Just like with anything, when you’re wondering about jitter... first get used to the sound of your system/gear as is. Then make a change and see if you hear any difference. If your DAC really does turn out to be "immune" to jitter... then changing USB cables (or whatever digital cable you’re using) should have no sonic impact. That’s an easy thing to test... just barrow a few alternate cables and swap. If you hear no difference at all, then that’s a coin in your "immune" jar. If you hear any difference at all, your DAC is not perfectly immune.

I’ll just say that I too had hoped that USB had finally found a way to defeat jitter by placing the master clock in the DAC and pulling packets etc. Well, at least with my DAC (Hegel HD30) USB cable swapping was clearly audible with a few cables I tried, and more dramatically, adding the PCT USBe in the path (between Aurender and DAC) has revolutionized the sound. A lot of marketing hype will throw out words like "immune" and perhaps your device is designed in such a way that it truly lives up to that claim. But even my Hegel DAC was supposed to be relatively unaffected by upstream jitter via USB given it’s design, and I’ve found that to be not the case at all.

p.s. I’m using the phrase "jitter" to broadly mean anything that allows the data to still arrive at the DAC uncorrupted, yet somehow the sound of D/A conversion is affected by other factors that are not digital in nature. Jitter (timing of the data) is most often discussed, but there are other non-digital variables as well such as noise. It’s entirely possible that what many of us hear and call "jitter" when changing cables and transports is really just changing the type of electrical/mechanical noise that gets sent along with the data to the DAC. Galvanic isolation is an example of a device that attempts to address this type of variable.
Benchmark DACs and a lot of others as well, "truly lives up to that claim", since the measured distortion and noise is well beyond what humans would hear. So if I use the word "immune" that's what I mean and if it is jitter a USB cable isn't going to fix it.
Wish I knew *exactly* what jitter sounded like. My system might be so full of jitter that it sounds like a garbage disposal to everyone but me, but how would I know? 
Best (and first) answer I found when researching “what does jitter sound like” came from John - 2009: 

“Like the sound of one hand clapping”.
Jitter creates sidebands to each frequency at very low level.  With a lot of frequencies (music) it is basically noise added to signal (inaudible without signal).  When I switched from CDP to Benchmark DAC1 I had impression of great clarity, that it took me a while to get used to.

The fact that sound changes with different cables might not have anything to do with jitter suppression since every connected cable injects electrical noise - some more, some less.