Which Might and Magic universe are you referring to?

I believe that the only way to connect two worlds is by placing them in the same galaxy.
I'm not sure what worlds existed in the old universe, but there were portals to Axeoth, so it's possible that there could be portals to Ashan as well (as someone here mentioned) - thus, heroes from the old universes could have ended up in Ashan. But this doesn't negate the unique culture and origin of Ashan.
There's no need to tie them to some "Ancients" or whoever. Let them exist side by side.