You have an internal drive cage for SATA, there are no internal cages like that for USB You can get an external drive with USB3 connection, take out the electronics, mount these at the end of your hard-drive in a regular mounting kit that just uses side brackets and run a cable to your USB ports from there.
Just get an adapter to mount the 2.5" drive in the larger bay for that. I though you were looking for someting with an internal USB3 connection so you can connect an external USB drive but mount it inside the case.
it had been my intent to raid the 2 sata ssd's on different raid channels. but even on a single raid channel, it should be enough to offset the slower write performance of SSD.
LOL.. i wonder what performance would be like if i used the icy dock raid striped on 2 128gb SSD's, then used the main board raid to raid those 2 SSD's with another 256gb SSD? 3 drives in 2 raids as a single striped device as an OS disk... i think that might be a bit of overkill.