Just a quick report. First some disclaimers:
- Testing was totally non-blind. Tough

- I used Toslink from MS200 and Coax from MS600 because I didn't have time to mess around with getting two SL Sooloos systems and the ID41 to all work at the same time through the same processor.
- The testing was done through an 861v8 which as the top M processor is likely to be most immune to the differences in jitter. Differences may be more apparent with other M processors.
I could detect a difference between MS200 and MS600 (both set to upsample as usual) but
only in some material. Acoustic recordings (such as Rattle's Mahler 2, a CD I've owned since 1989 and which I use as one of my main test discs) show a more substantial image and better imaging with MS600. However, listening to non-acoustic (Melody Gardot, another oft-played test disc) the difference was not really detectable. As mentioned, into a different processor the difference
may be clearer.
The jump from MS600 to ID41 is clear in all material. The ID41 gives a huge soundstage, clearer imaging, better separation of instruments, and more realistic timbres.
Summary: if you have a 568 or G-series processor and want to get the best out of Sooloos, audition the MS600 against the MS200 in your system. Depending on your system and listening preferences, it may be a worthwhile upgrade. Or not.
PS: In analogue, into my Stax headphones, the differences between MS200 - without Prime PSU - and MS600 are obvious. For analogue usage the MS200 is convenient but the MS600 is far superior, sounding wonderful into the Staxes.