Whats causing the dramatic difference?
To be honest, an SSD in a the BDP-2 is probably a waste of time. You will get no extra benefit except no moving parts. Even a green magnetic drive will easily exceed the throughput of the BDP which has somewhat limited processing power.
Therefore the network performance to and from the ssd is limited by the processing power of the BDP-2 rather than the interface or core speed of any drive connected.
It isn't really an issue as even a 192KHz lossless file is unlikely to require more than 1MB/s where it is loaded into memory, and then from there it is decoded and output as a PCM signal (i.e. your source whether a drive, network source, USB is irrelevant).
Have an 8 bay QNAP NAS that can easily sustain 100+MB/s transfers and it only benchmarks on the BDP-2 at 9MB/s.