Try reversing the approach you're using to try to match the one machine+drive. Instead of doing (NOT machine AND NOT drive), uniquely identify the machine/drive you want filter and NOT that, i.e. NOT (machine AND drive).
So
WHERE
(tblAssets.AssetUnique NOT LIKE '%1ip-08%' AND tblDiskdrives.Caption NOT LIKE '%E%')
AND Cast(Cast(tblDiskdrives.Freespace AS bigint) / 1024 / 1024 AS numeric) < 1024
AND Cast(Cast(tblDiskdrives.Size AS bigint) / 1024 / 1024 AS numeric) <> 0
AND tblComputersystem.Domainrole < 2
AND tblDiskdrives.DriveType = 3
AND tblAssetCustom.State = 1
becomes
WHERE
NOT (tblAssets.AssetUnique LIKE '%1ip-08%' AND tblDiskdrives.Caption LIKE '%E%')
AND Cast(Cast(tblDiskdrives.Freespace AS bigint) / 1024 / 1024 AS numeric) < 1024
AND Cast(Cast(tblDiskdrives.Size AS bigint) / 1024 / 1024 AS numeric) <> 0
AND tblComputersystem.Domainrole < 2
AND tblDiskdrives.DriveType = 3
AND tblAssetCustom.State = 1