@bold No one said he was going to absorb it directly to himself, I was referring to using PS as a vessel.
@Underlined The chakra of Shinju wasn't either it was from the Shinobi Alliance but he was able to take it in, the Bijuu chakra weren't apart of Sasuke yet he was able to absorb it.
No, IT is not what allows the chakra absorption, Shin: Jukai Kōtan does. IT placed everyone under genjutsu while the latter absorbs their chakra which works exactly like the Shinju but on a larger scale.
Sasuke used his PS as a replacement for the Gedo, he didn't take in the chakra directly he used it like a container which allowed him to use it as if it was his own so in this case it would be the same for Madara.
@Bold Already agreed that Madara himself cannot handle all that chakra if he were to absorb it directly.
Addressed.
Sasuke didn't absorb but rather sealed the Bijuu into his PS. Madara was able to absorb the Shinjuu just like that because he was the Juubi Jin. The Shinju is a part of the Juubi. Obito let it out during his time as a Jin and Madara simply took it back when he became the Jin. Sealing and Absorbing are two different things.
One could seal something into something else. Sasuke sealing the Bijuu into his PS/Minato sealing Kurama into Naruto/Itachi sealing Orochimaru into Totsuka. Absorbing involves becoming one with something else (adding it to yourself). In this case, Madara was able to absorb the Shinjuu since it was already part of the Juubi (they became one again). Absorbing chakra involves going into the user's body since that's what absorbing is and then they use it however they desire since it's now their chakra.
When Madara absorbed the Shinju, he didn't become "one" with it. It became "one" with the Juubi that was sealed inside him (Kurama still existed as a seperate being inside of Naruto since he was sealed which is why I mentioned two seperate sources of chakra). Being sealed inside of Madara meant that Madara could use the power and chakra of that creature sealed inside him. Sasuke sealing the Bijuu into his PS still allowed him to use the power and chakra of the Bijuu sealed inside his PS (though only his PS since it was used as the vessel for all 9 Bijuu) Regardless, they still exist as seperate beings. Absorbing something involves that something becoming a part of you.
This is why even if a different technique was used to absorb that chakra, that chakra would still go into the user first since that is what absorbing does.
That's why I highly doubt Madara could use the chakra of the IT victims until he absorbs that chakra. That chakra first has to go into himself before he could use it. He has to absorb it if that's what the technique does.
The only thing I'm certain that Madara could do is either release the Juubi (or Bijuu) and seal it into his PS or replenish his chakra constantly after every use by absorbing the chakra of the IT victims.
Sorry for the long response if you read this far.