Thanks for the reply.
Using two backplates isn't going to work really. The adapter is for a shuttle which only has two expansion slots in total, and I'm planning on putting a gfx card in there too. After doing some more research it seems that most external SATA housings have a power port on them anyhow, so I could always power the drives from another source. Probably not wise to overload the shuttle's PSU anyway, esp. with a gfx card in there too.
I know you can't link to external sites, but could you perhaps suggest a google search string that might lead me in the right direction?
Thanks.