"BS!
You cannot silence a super-sonic projectile!
(More physics, less BS)"
Sure you can. Just slow it down. Which it's going to do of its own accord anyway ...eventually.
This rifle only has a 10" barrel with a 6" permanently-attached muzzle device (the suppressor). Any permanently-attached muzzle device is included in the BATF's accounting for total barrel length, which is how this weapon dodges the additional $200 tax for a short-barreled rifle.
Most "standard velocity" .22LR is subsonic when fired from a barrel as short as 16" (
all .22 match ammo is), and I dare say even most "high velocity" ammunition will be subsonic from this 10" barrel. So I think you could shoot most any ammo you want from it and it still will be subsonic at the muzzle.
If it isn't SSS, it's easy to tell even without a chrono because the crack of the supersonic bullet makes a very discernible echo. It can be difficult to hear the difference with an unsuppressed rifle because the muzzle blast (which is only a couple of feet from the shooter) overpowers the echo (which is coming from some yards away) but with a suppressor, you can hear the echo of every shot that's supersonic (unless you're in the middle of the Bonneville Salt Flats and there's nothing within a mile for it to echo off of).