John, have you tried the Sooloos spdif direct to the benchmark (unless one of your trials below includes that but I am presuming your spdif mentioned below is the spdif out from the MS600 itself). Since I have a dac with spdif input already if this performance is also identical (though unlikely) it might mean the MS600 is also not needed.
Not sure I understand the question Howie. If you mean SPDIF ex Control:10 then NO, I have not auditioned that and have not been tempted because, the dealer indicated it would not be as good as from the MS600. Now the Control 15 is a different beast and there is most likely no difference between SPFIF from it or from the MS600.
I guess it all boils down to what item is doing the apodising, upsampling etc. If the Control 15 was doing that and the MS200 was merely the conduit for the "purified" digital output then I guess the MS600 would not be needed. But I'm out of my depth here as I'm unsure exactly what the MS200 does. All I can say is that the MS600 is a super item in the system here.
John