Substitute for your 
RemainingPercentage.
Select Top 1000000
  tblAssets.AssetID,
  tblAssets.AssetName As [Printer Name],
  tblAssetCustom.Custom11 As [MT Asset Tag],
  tblAssets.IPAddress As [IP Address],
  tsysIPLocations.IPLocation As [Facility Location],
  tblAssetCustom.Manufacturer,
  tblAssetCustom.Model,
  Convert( VarChar(10),
         Cast( Case
                 When tblCustDevPrinter.TonerMaximum > 0
                 Then tblCustDevPrinter.TonerRemaining / tblCustDevPrinter.TonerMaximum * 100
               End
         As Decimal(6,2))) + '%' As RemainingPercentage,
...
The funny thing is, you've handled it in your WHERE clause. You could just as easily copy your code from there to use as the 
RemainingPercentage value.
Select Top 1000000
  tblAssets.AssetID,
  tblAssets.AssetName As [Printer Name],
  tblAssetCustom.Custom11 As [MT Asset Tag],
  tblAssets.IPAddress As [IP Address],
  tsysIPLocations.IPLocation As [Facility Location],
  tblAssetCustom.Manufacturer,
  tblAssetCustom.Model,
  Cast(Floor(tblCustDevPrinter.TonerRemaining / (Case
                                                   When tblCustDevPrinter.TonerMaximum = 0
                                                   Then 1
                                                   Else tblCustDevPrinter.TonerMaximum
                                                 End) * 100) As nvarchar) + '%' As RemainingPercentage,
...