You have a classic case of PCI latency / bus utilisation issues with Creative (all of them) cards.
They are very prominent on Via chipsets, but sometimes also rear their ugly head on Intel/nvidia/AMD chipsets.
The issue is, as described, PCI bus control devices battling for long enough time to lock the bus transfers.
You can remedy this, as Iron dreamer explained, by raising your sound card PCI latency and lowering that of your RAID's. You'll loose some of the throughput on that RAID card.
Any PCI card will be the same, if it uses the same chipset. Better cards can co-exists without problems on the PCI bus, without completely hogging it or being starved when others behave not so nicely.
You can also try raising the internal buffer of your sound card. This could alleviate things a bit as well (I'm not sure EMU has one, but I use one on my RME).
There are also motherboards that have a dedicated higher PCI latency PCI slot in them, meant for audio cards. Some people have found that these work also nicely, without having to fiddle with PowerStrip.
This is also the reason why I like my RME card: no clicks, pops - ever on any of my chipsets/motherboards, regardless of how many IDEs I've run (8 devices maximum).