Out of pure interest...

[WinsingtonIII]

furthermore the chinese huge army would represent a big burden to feed and have available water while going trough euroasia so it´s very likely that such a burden would undoudabtly end up with civil strifes and rebellions in china

Who says the Chinese would be invading the Roman Empire? If anything, given the expansionist tendencies of the Romans it would more likely be the other way around, and in my opinion the defender has the inherent advantage here. With two massive entities like this, it's not going to come down to tactics, weaponry or generals, it's going to come down to attrition. In the expanses of the Western Chinese steppe, it doesn't necessarily matter if the Romans win battle after battle, they still have to keep marching forward into hostile, unforgiving territory inhabited by a hostile population. Plus, I do not doubt the nomads would take the opportunity to raid the supplies of both sides, but the Chinese do not have as far to go to resupply. By the time the Romans reached the major population centers further East they would be demoralized, exhausted, starving, and their forces would be depleted from the toils of the journey and nomadic raids. The Central Asian Steppe is simply not the kind of terrain you march an army across and expect them to come out on the other side ready to fight (unless your forces are nomadic and used to that lifestyle). As such, if the Chinese were the ones to attack, they would most likely lose as well. But in my opinion, if this were to ever happen (very unlikely in the first place), it would have been the Romans doing the attacking, not the other way around.