I've had poor experience with the Marvell based chips (see my recent post which really should have been in this thread - sorry!). Here are a couple of threads related to Marvell + port multiplier support:
I've also seen controller lockups on the Marvell AHCI controllers unless NCQ is disabled.
SATA Port multipliers seem to provide limited bandwidth and are a little fiddly to support in hardware and software, so I'm wondering if a solution based on PCIe switches wouldn't be better? You can then use the fast/wide PCIe slots that many motherboards have at least a couple of, together with commodity SATA controllers.
The sil3132 is pretty good, but is only PCIe 1.x and coming to end-of-life.
The sil3124 is a PCI-X design now fronted by PCIe to parallel PCI bridge chips, and are either very expensive (x4 designs) or slow, and seem like a weird way to do things.
I've found the Marvell chips unreliable (perhaps newer ones are better, but I just didn't like their general attitude much - e.g. no errata released except under NDA!).
Similar with LSI (buggy and bad attitude).
The ASMedia 1061 seems promising, but I haven't any experience of it with SATA port multipliers (to fit in to 1.0 -> 3.0 pods), very cheap with good performance - but limited to 2 ports (PCIe 2.0 single lane), so of limited use unless behind a PCIe bridge
Backblaze have gone for the Rocket 750 of course - this uses a Marvell 88SE9485 (8 port SATA/SAS PCIe 2.0 x8), together with (I assume) eight 5 port Marvell port multipliers - giving 120 MB/s per SATA port. Pricey tho', and Marvell have given me so much hassle in the past that I'm reluctant to go with them again...
"SATA Express" (essentially hard drives which speak PCIe directly instead of SATA) may make things more interesting, if the uptake is quick enough...