Power Mac 5500, PCI Sound.. Options

Hi There! I'm setting up a Powermac 5500+ machine for hard disk recording, and I've run into a problem. The 5500 only has one PCI slot. I want to install a good sound card, but I don't want to limit the machine by not being able to expand it any further.
If I install a USB 2 or FireWire card to the PCI Slot, would I be able to run an external sound card / box with this machine? Have any of you used external sound cards with older Macs with any success ? The basic specs of the machine are 250Mhz 603e with 64 megs memory running OS8, but will be updateing to 128 Megs (the systems max) and OS8.x or maybe OS9 if it will take it..
A newer system is not an option here.

Thanks up front for any advice / opinions any of you fine people may offer.
Tom

[Synthetic]

I agree with Saurabh on the OS for 5500. I would just get newest version of OS 8 to use and stay away from OS 9 as it will eat more cpu cycles and OS 8 was much more stable than the previous OS systems. Also, the Audiomedia III cards could be a good choice but... getting USB or firewire PCI will give you at least 2 ports which is nice for using one with audio interface and still leaving one for use with another device.