It sounds from the respective data transfers that there are a lot of errors on the network, which is causing the receiving end (the Sooloos) to repeatedly tell the sending end (the MBP) to re-try ... hence the 17MB received by the MBP, and the big transfers to the Ensemble.
Under TCP/IP if the receiver gets bad packets it returns an error, forcing a re-try on the transmission after an arbitrary wait period. The result is that everything arrives ... eventually. But it's really slow.
This smells to me like either a faulty cable or a faulty network switch, and of the two I'd tend to suspect the switch - in my experience cables either work or they don't, and tend to get worse over time rather than showing steady-state poor performance.
The other possibility is that there's a network device spewing bad packets onto the network, but if your Internet connection is working normally then this seems less likely. So the advice to get the laptop and the Ensemble into the same room with a cheap switch seems like a good one.