gary
i can't speak for RAID with DP/Kontakt/DAE - but i personally feel that RAID isn't designed/intended as a solution for sample streaming. RAID is all about throughput and sample streaming is basically all about seek time.
so what you have right now - multiple drives - is the best solution for sample streaming (though, with logic, multiple drives don't improve performance - i wouldn't be surprised if kontakt/DP/DAE actually benefited from multiple drives). your current problem is merely a 'bus' limitation.
are you thinking about the apple RAID so that you can recycle your current ATA drives that are inside the firewire cases? or are you buying it straight up, with new drives and all? can the apple RAID not be used as a RAID - but as multiple drives? if so, that could be a great solution.
but if not, perhaps you should consider buying multiple SATA drives, an external SATA drive enclosure, and an SATA PCI card, like this
http://macgurus.com/prod...pages/sata/tsata-x44.php"="" target="_blank" title="http://macgurus.com/productpages/sata/tsata-x44.php">http://macgurus.com/productpages/sata/tsata-x44.php">http://macgurus.com/productpages/sata/tsata-x44.php. 300+ MB/sec bandwidth, up to 8 external ports, one PCI slot.
that would give you the bus bandwidth you need and preserve independent seek times of all the drives (all drives wouldn't have to be involved with delivering all samples).
i've found the macgurus (the company linked to above) to be very knowledgeable and helpful - and, if you want, they will build a system to suit.
unfortunately, i'm not aware of any (non firewire) multi-drive ATA enclosures.
if the Apple Raid can be run as independent, unraided drives - then that is probably the simplest solution (you can then see if the RAID improves/degrades/doesn't matter for performance vs. multiple drives) and keeps the troubleshooting to a minimum (call apple).
but if it can't, consider emailing the macgurus. also check out xlr8yourmac.com for reports on any SATA PCI cards.
if you decide to go RAID, you could also consider contacting the people at hugesystems.com and asking if you can buy one of their RAID enclosures. they have at least one which uses ATA drives. so you could recycle your drives and just add a scsi card to the G5. but they are hardware RAID, so you'd have to use the drives striped.
anyway, hope this helps. whatever you choose, please report back with real world experience.
the DP/kontakt option is a compelling one.
cheers