Run yourself a list of what's in tblAssetCustom.
SELECT Distinct Top 1000000
tblAssetCustom.Manufacturer,
tblAssetCustom.Model
FROM
tblAssetCustom
You should be able to use what you find in there to filter on the manufacturer and/or model. E.g. with my inventory, I can include
AND (tblAssetCustom.Manufacturer Not Like 'VMWare%')
AND (tblAssetCustom.Model Not Like 'VMWare%')
AND (tblAssetCustom.Model <> 'Virtual Machine')
in my WHERE clause. (I could get away with just checking the model, but I like to cover all my bases.)