Windows 8 VMs will not work yet. There is alot of work needed to support the Lync VDI plugin with the Lync client running inside a Windows 8 VM.
The fact that it doesn't work with RDP either leads me to believe this is a configuration issue.
Can you also check if the following file exists on the VM?
Program Files > Microsoft Office > Office15
"LyncTSProxy.dll" file