First make sure that you have the correct version of ALSA installed (for the SB Extigy/Audigy, this is 1.0.9). The alsa_usb module relies on the alsa device names. /proc/asound/cards lists the number and name of each recognized soundcard:
~ # cat /proc/asound/cards
0 [Extigy ]: USB-Audio - Sound Blaster Extigy
Creative Technology Ltd. Sound Blaster Extigy [...]
1 [I82801DBICH4 ]: ICH4 - Intel 82801DB-ICH4
Intel 82801DB-ICH4 with AD1981B at 0x24000800, irq 11
2 [Modem ]: ICH-MODEM - Intel 82801DB-ICH4 Modem
Intel 82801DB-ICH4 Modem at 0x1400, irq 11
You need to pass the number or name prefixed with a hw: to lircd. In this case lircd -d hw:0 or lircd -d hw:Extigy. It is recommended to use the name, since it is independent of the order in which the devices are discovered and lircd will exit, if the Extigy is not connected.