I just wanted to report a success story, since I've been using this configuration with only minimal problems for over a month.
Under Windows XP Pro, I'm using the Mediasonic 4-bay (non-RAID) drive enclosure via its eSATA connection (the enclosure also supports USB 3.0, but I haven't tested that yet). I'm running this on my Compaq laptop (with an AMD Athlon 64 Processor) using a Syba SD-EXP40014 eSATA ExpressCard and it recognizes all 4 drives in the box off a single eSATA cable. You need to have an eSATA card that supports port replication, which my Syba card does (so do some other Syba cards, as well as some StarTech cards, but I haven't tried those).
Also when I had one of the drives in a separate single drive enclosure, HDS recognized both the single enclosure and the remaining 3 drives in the Mediasonic box (using a total of 2 eSATA cables connected to the 2 ports on the Syba ExpressCard).
The only problem I've had was when I moved drives into the bay or removed them from the bay into another enclosure. It normally takes either a manual shutdown and restart of HDS, a reboot of my computer (or maybe both) to get everything recognized in its proper location. But so far, HDS has always eventually recognized all the drives. This delay in recognition may be a flaw of HDS, or something inherent with having multiple drives through one eSATA cable. However the Windows Disk Management applet (through the Control Panel | Administrative Tools | Computer Management) always seems to properly recognize the drives before HDS does, so I'm guessing the fault is at least partially with HDS (mildly annoying, but now that I know it's an issue, I know to expect it).
So a general recommendation is when you connect a new enclosure and/or drive that HDS doesn't seem to know exists, make sure you try quitting and restarting HDS, and probably also rebooting your machine a second time to make sure everything has a chance to be recognized.