ITNW isn't real immunity, it means they have Hardened Armor equal to Force x 2.
Hardened Armor means that you MUST do damage greater than the armor value or the target takes no damage. Armor piercing or similar effects (such as Elemental damage halving armor values) count to get through the Hardened Armor.
So a Force 5 Spirit has 10 Hardened Armor, which means you have to do at least 11 damage for it to notice.
But this could, for example, be done with a Ruger Super Warhawk (6P, -2AP) if you make at least 3 net hits (9P damage > 10-2 Armor) or, even easier with a simple Stick'n'Shock round doing 5S(e)+1 from a net hit vs 10/2 Armor.
So you CAN shoot the bastards, just make sure to do enough of it at one time. Called Shot for extra damage help a lot if your weapon is too weak. And don't forget that extra Damage from bursts does NOT count towards armor piercing.