I don't think there's an easy way to cascade all the way down the chain with SQL, but this sample report lists managers and the computers of two levels of "direct reports".
Select Top 1000000 tblADusers.Username As Manager,
tblADusers.Userdomain As ManagerDomain,
tblADusers1.Username As DirectReportLevel1,
tblAssets.AssetID,
tblAssets.AssetName As Lvl1Asset,
tblAssets.Domain As Lvl1Domain,
tblAssetCustom.PurchaseDate As Lvl1PurchaseDate,
tblAssetCustom.Warrantydate As Lvl1WarrantyDate,
tblADusers2.Username As DirectReportLevel2,
tblAssets1.AssetName As Lvl2Asset,
tblAssets1.Domain As Lvl2Domain,
tblAssetCustom1.PurchaseDate As Lvl2PurchaseDate,
tblAssetCustom1.Warrantydate As Lvl2WarrantyDate
From tblADusers
Left Join tblADusers tblADusers1 On tblADusers.ADObjectID =
tblADusers1.ManagerADObjectId
Left Join tblAssets On tblAssets.Username = tblADusers1.Username And
tblAssets.Userdomain = tblADusers1.Userdomain
Left Join tblAssetCustom On tblAssets.AssetID = tblAssetCustom.AssetID
Left Join tblADusers tblADusers2 On tblADusers1.ADObjectID =
tblADusers2.ManagerADObjectId
Left Join tblAssets tblAssets1 On tblAssets1.Username = tblADusers2.Username
And tblAssets1.Userdomain = tblADusers2.Userdomain
Left Join tblAssetCustom tblAssetCustom1 On tblAssets1.AssetID =
tblAssetCustom1.AssetID
Order By ManagerDomain,
Manager,
DirectReportLevel1,
DirectReportLevel2