Did my best to find a quick/cheap platform you can experiment with. This is an example of an underpowered SoC. Even though the board itself supports SATA 2.5, USB 3, and Gig-E, the CPU can't. Obviously, it doesn't fulfill your needs, but you can run benchmarks to figure out what you actually need based upon it.
- Pogoplug v4 -- ARM-based, runs linux. $19.
- Take a look at this -- it appears that uboot supports port multipliers on the PogoPlug (although it may be picky).
- Here's some info on performance tuning for the PogoPlug.
- One random person's findings for you, which may be useful: http://www.amazon.com/review/R19Z6KK1PE094C/ref=cm_cr_pr_perm?ie=UTF8&ASIN=B006I5MKZY