Is it supported to have two Ultra 320 docks striped together?  Not daisychained but having each in single bus mode on it's own scsi controller and then striping the 24 drives together?  The set up guide isn't clear on this

 Yes, this is an approved setup.  Each chassis is set to Single Bus Mode, and you can create (up to) a  24-drive stripe set.  On xw8000's and xw8200's you can connect to the onboard LSI SCSI Controllers, using the SCSI Extender Kit from HP.  On xw8400's and xw8600's you'd need to add an ATTO UL4D Dual-Channel Controller.

thanks.  I talked to someone at Avid that said that you won't get the max 2 streams of uncompressed HD with this set up because the docks are in single bus mode as opposed to dual bus.  But we need the storage of two chasis so we have to go with this set up

I'm not (completely) convinced that explanation is accurate.  With this config, you're still using dual-busses on the SCSI controller, and 1/2 drives are on each channel.  The only difference is that you'll have 12 drives per channel, instead of 6.  Unless the channels get "saturated" prior to 12 drives, this should easily provide the bandwidth.  We typically got 280MB/s + ....

yeah that's what I figured.  You can still stipe the 24 drives across the bus