If ShoutmonX4 is deleted, either after the attack or in opponent's turn, the "Material Save 2" is triggered. You can choose 2 Digimon from ShoutmonX4's digivolution source to put under 1 of your tamer, for example: I would pick Shoutmon for "Rush" and Ballistamon for "Piercing" to be saved-material, place them under Mikey Kudo tamer.
For Mickey Kudo [Your Turn] effect, "when playing 1 of your Digimon with DIgiXcros requirements, by suspending this Tamer, you can also place cards from under your tamers into digivolution source by DigiXcros".
The question is: If I use the Digimon under Mickey Kudo to place under a DigiXcros Digimon, can I reduce play-cost of that DigiXcros Digimon by 2 for each card I placed from the Tamer.
The answer is : yes.
The reduce-play-cost is applied for all those Digimon that listed in DigiXcros requirement, no matter they are taken from the battle or under a tamer, as long as there is no duplication. So ShoutmonX4 can be played by paying 1-cost minimum.
In the case if ShoutmonX4 is not deleted after the attack, you can choose to trigger its "end of attack" effect if you have another ShoutmonX4 in hand. It allows you to place all its digivolution cards under 1 of your tamer in any order to unsuspend 1 of your tamer, and if you do, delete the ShoutmonX4.
This step helps to preserve all the Digixcros materials to do another DigiXcros for another ShoutmonX4. As long as you have enough memory, the new ShoutmonX4 can attack opponent's Digimon or player with "Rush" inherited from Shoutmon.