You can get single port GbE PCIe adapters, and these do perform better than PCI ones, although it will often take good drives / RAID (on an internal LAN of course) to see the difference. (But if you have a crowded PCI bus, esp. with an add-on storage controller -- then the difference might be easily noticable.)
Another option would be USB -- USB wireless would probably make more sense than PCI / PCIe, and USB sound is also widely available.