Since you're actually wanting two different sets of data (assets with 
software_name and assets without 
software_name), I think you're going to need to create a union of two data selections. Substitute the software name and version that you're looking for, of course.
-- those assets with the desired software and maybe the right version
Select Top 1000000
  tblAssets.AssetID,
  tblAssets.AssetName,
  tsysAssetTypes.AssetTypename,
  tsysAssetTypes.AssetTypeIcon10 As icon,
  tblAssets.IPAddress,
  tblAssets.Lastseen,
  tblAssets.Lasttried,
  tblSoftwareUni.softwareName,
  tblSoftware.softwareVersion,
  Case
    When tblSoftwareUni.softwareName Like 'software_name%' And tblSoftware.softwareVersion = 'wanted_software_version'
    Then '#ccffcc'  -- green: good name and good version
    Else '#ffcccc'  -- red: good name, but wrong version
  End As backgroundcolor
From
  tblAssets
  Inner Join tblAssetCustom On tblAssets.AssetID = tblAssetCustom.AssetID
  Inner Join tsysAssetTypes On tsysAssetTypes.AssetType = tblAssets.Assettype
  Inner Join tblSoftware On tblAssets.AssetID = tblSoftware.AssetID
  Inner Join tblSoftwareUni On tblSoftwareUni.SoftID = tblSoftware.softID
Where
  tblSoftwareUni.softwareName Like 'software_name%'
  And tblAssetCustom.State = 1
  And tblAssets.Assettype = -1
Union
-- those assets without the desired software
Select Top 1000000
  tblAssets.AssetID,
  tblAssets.AssetName,
  tsysAssetTypes.AssetTypename,
  tsysAssetTypes.AssetTypeIcon10 As icon,
  tblAssets.IPAddress,
  tblAssets.Lastseen,
  tblAssets.Lasttried,
  Null,
  Null,
  '#ffcccc' As backgroundcolor  -- always red; software not installed
From
  tblAssets
  Inner Join tblAssetCustom On tblAssets.AssetID = tblAssetCustom.AssetID
  Inner Join tsysAssetTypes On tsysAssetTypes.AssetType = tblAssets.Assettype
Where
  tblAssetCustom.State = 1
  And tblAssets.Assettype = -1
  And Not Exists(Select tblSoftware.AssetID
                 From tblSoftware
                   Inner Join tblSoftwareUni On tblSoftwareUni.SoftID = tblSoftware.softID
                 Where
                   tblAssets.AssetID = tblSoftware.AssetID
                   And tblSoftwareUni.softwareName Like 'software_name%')
Order By
  AssetName