The PERC6i was also offered on the T7400 (successor to the 690) and is currently also offered on the T7500 (successor to the T7400). Neither of these 2 systems have a backplane for the drives, so there can't be a requirement for a backplane.

The first thing that comes to mind is a faulty cable.

Does your cable have a sideband cable (not connected to anything obviously)? Even though you wouldn't think it would affect it, but maybe it's causing the adapter to think it should have a backplane.

I found a similar post which seems to suggest that all I need is a 8484 to SATA cable and that should do it.

http://en.community.dell.com/support-forums/servers/f/906/p/19295942/19557807.aspx

The cables I have appear to be good quality (coincidentally with HP replacement P/N).  Odd that two of them would not work.  

Anyone have insight into this configuration? Do all drive cables need to be populated, etc?   I do remember that when installing in the R710, I had to have both backplane connectors connected before the card would recognize the drives.  I will try a couple different configurations in the mean time and see if I get lucky.

Here is a link to the cable I purchased - doesn't seem to be much to it.

http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&rt=nc&nma=true&item=220680145480

It was described as SAS Controller to 4 x SATA Cable HDD Splitter Cable 32-pin SFF-8484 to 4 x 7-pin internal Serial Attached SCS(SAS) cable.

I purchased two of them.  The connector mates with the SAS ports on the PERC 6i and neither seem to work.  Also have now tried on a SAS 6ir, same thing.

I suspect from your question that I may need a different cable.  These seem pretty simple, without sideband cable.  Do you have any insight there?

Thanks and Best- 

Did you ever get a Perc 6/i adapter to see SATA drives via a direct connect 8484-SFF cable to 4 x SATA connectors? Thanks for any information.