Let's start with how Madara can use Susanoo without his eyes.
http://narutobase.net/manga/Naruto/619/15
This explanation by Tobirama pretty much says that the Sharingan you see is caused by special chakra in their brain unique to the Uchiha. So the chakra in their brain is the source of the Sharingans power and the actual eye is simply the way in which the chakra dispenses for MOST of it's abilities like genjutsu and Amaterasu, two special jutsus that require sight and visual contact to utilize.
Susanoo does not need to be dispensed through the eyes. Proof of this is the fact that susanoo does not cause the eyes to bleed like here.
http://narutobase.net/manga/Naruto/392/2
You need to awaken both mangekyou sharingans to unlock Susanoo, but once it is unlocked it no longer needs the actual eyes to be used. Notice Itachi's eyes aren't even using Sharingan while the Susanoo is active.
My theory is that Susanoo only needs the chakra within your brain to activate after its initial activation. Many jutsus are like that, at first they require hand seals to activate but over time their bodies adapt over time after they use it a lot. I believe Susanoo is the same scenario.

My second explanation is to how Madara is simply surviving every hit made to him. The answer to me is simply Hashirama's cells.
http://narutobase.net/manga/Naruto/657/8
If you remember in previous chapters Hashirama and Madaras fight, as explained was on a scale beyond any normal human. Their battles altered the terrain of the very land they fought in. Their battles could be seen as battles between two tailed beasts, which they were in a way as Madara was controlling the Kyuubi and Hashi had his Mokuton - Wood Dragon.
http://narutobase.net/manga/Naruto/620/16
This kyuubi was full sized by the way. Not a half size Naruto controls. There were TBB be launched by this complete Nine-tails and both didn't really make an attempt to dodge even though they were clearly humans and alive.

Following that logic, if Madara who had could withstand power like that and not be affected than it shouldn't even be questioned why he isn't being beat down by 8 WEAKER tailed beasts than the nine tails he was controlling like nothing.
Now all that power PLUS Hashirama's cells and chakra pretty much makes him the closest thing to the sage without using all the extra power of the juubi.