Hello,
To check this further can you plug different PCI device that is supported by NetBSD and check if it works? The problem maybe alsa related to the atheros card only.
What about the OpenBoot of Solaris? Are you able to run some device test before booting NetBSD (you must need probably original SUN keyboard to access that).
Sorry but this is quite unusual problem- try asking
port-sparc64@netbsd.org also.
Kr,
Piotr.