I believe that the MSB RJ45 is their "network" connection, not an S/PDIF connection, so the jitter rules probably do not apply. the short cable is actually better.
One BIG improvement that you could probably make is to put a Superclock2 in your 7700 transport. I did this in my reference transport. Since the MSB upsampler is synchronous, it only relies on the transport and its clock. This makes the clock jitter in the transport even more critical.
In my system, the upsampler is asynchronous, so it is reclocked on the oscillator in the upsampler in the P-3A.