I'll talk in general about my experience.
I have used the Wyred4Sound DAC1 using the ESS Sabre. Despite all the marketing spin, it is still susceptabe to incoming jitter. Even if its jitter reduction is better than some, feeding it, or any DAC with a the lowest jitter source you can, will be beneficial.
I use a teralink X (the original one using the CM108 USB receiver). Many knowledgeable people have said that this is a high jitter chip. I agree with that, but what I have found is that its sound quality, and presumeably its jitter rejection is based upon the power feeding the CM108 itself and the 12Mhz crystal that feeds the clock to the CM108. So I have modded it in the following ways, I have put OSCON SEPC capacitors all through my Teralink, I have replaced the balanced line driver chips the feeds the SPDIF output with the faster 4ns latency chip (original chip is a 20ns latency chip), run some small film foil capacitors from either side the inductor feeding the crystal to ground, desoldered the toslink connector from the board, as I dont use toslink, and it consumes power and creates pulses on the power rail. I also feed the teralink with a JLH ripple eater low noise power supply.
After doing all this, it really sounds nothing like the original. Before these mods it did have flabby bass, and an overly warm sound, but now the bass is tight and the highs are crystal clear, depth of sound, and detail level is excellent.
Another thing I do is use CMP +cPlay as a source, but not only that, I remove unused drivers and remove unnessecary stuff from the registry, doing all this makes CMP even less jittery. The improvements to the sound are amazing.
Information on this can be found on the CMP forum at audioasylum.
I'm also considering getting the AudioGD unit, but the sound i'm getting at the moment is so darn good that I wonder how much better it can get. I notice that not many people mod the cheaper USB>SPDIF converters, and most reviews are based on stock standard units. I think my modified Teralink X would stand up quite well against even the Teralink X2? only problem is my X1 does not do anything above 16bit/48khz.