I don't know about disc drive brands other than HP/Seagate and EMC arrays. I
have put a drive case on top of a cabinet without problems. These where
older drives that shook more than the new ones, so your probably safe.
I don't know if you've looked into I/O expansion cages on your 9X9s. Your
supposed to be able to double your F/W I/O ports. This may allow you to have
fewer drives per channel.