You might want to make use of Custom Properties.
[Start > Programs > SolarWinds Orion > Grouping and Access Control > Custom Property Editor]
And create a Custom Property for Volumes, and group all drives that are mapped to NAS.
E.g. a Yes/No Custom Property called NAS
Back to the Trigger Condition of the Advanced Alert, you can use the following:
Trigger Alert when ALL of the following apply:
Volume Percent Used is greater than 99
VolumeType is equals to Fixed Disk
ServerType is equals to Physical
NAS is not equals to Yes
Thanks that worked..