Does it not already have a form of suppressor within the shroud end? Considering that springers are relatively quiet, and that the shroud will further reduce the sound, perhaps it is not necessary. Much of the noise you hear would be mechanical noise, try (safely) listening to the gun's actual report downrange with someone else firing it.
There must be a reason one almost never (well, personally, I never) sees this gun with any form of moderator on it.