You can try giving CalDigit a call, (I used to work there), but I'm pretty sure that the speeds you're seeing are within "normal" parameters. The 220MB/s speed you indicated wanting to see is a "theoretical maximum" speed & you wouldn't necessarily expect to see that, especially out of a 2 drive RAID 0 setup. 4 drives would likely give you a bit more speed, (if they were in 1 enclosure) but not much more....
Hope this helps.
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