Cubase crash with dual 500mhz, Frequent audio and mide crashes -Cubase Options

[sugarplum]

I run a Dual 500mhz G4 with Cubase, Reason and a MOTU 2408. Connected to it I have two monitors a Viewsonic PT813 on an Rage 128 AGP and a 19' Lacie on a Radeon 2000 PCI, a ASANTE USB HUb-7, Steinberg USB 2-2 midi interface with various units I use for input including the oxygen 8.
Since installing the radeon card and firmware (ATI is of no help) I have had numberous intermitent crashes with Cubase 32 (5.1r1) (Steinberg of no help either). I am on my third replacement card so I think I've ruled out a defect. The audio masters drop out in Cubase while the meters still read on the individual channels. To get them to work again I have to either restart Cubase (which doesn't always start without freezing) and/or change my input settings to Sound Manager and then back to MOTU. This is aside from my midi input desiding to stop reading in Cubase (happened previous to second monitor config).
Sorry for the long winded explanation. Any ideas?

Greg