the card reader is for memory cards, so you can take pictures from your digital camera or phone or whatever without the lead,
you can buy adapters to convert usb to firewire and vice versa <'usb firewire adapter' into ebay search> but i have NO IDEA AT ALL how good an idea this is for audio equipment.
personally? i don't think it sounds like a healthy way to connect audio gear
especially if your audio device is firewire,,,cos chances are usb will not be fast enough to communicate with it effectively....