While not a direct answer to your question, this [http://www.tomshardware.com/reviews/silicon-image-brings-virtualization-esata,1610-3.html|Tom's Hardware article] has a lot of pertinent information.
Specifically:
"If your SATA controller does not recognize PMs, it will run all attached hard drives as if they each were attached to a separate SATA port."
"Port multipliers can be used to run up to 15 SATA drives via a single SATA connection. Hardly anyone would operate so many drives over a single connection, because the 300 MB/s link will become a bottleneck."