First, I have read the IDW flashbacks (I get asked this a lot). And I loved it. That two-parter only did show how they got together, and nothing beyond that.
My headcanon is rather close to the IDW flashbacks, though they have existed long before the comics. It is only natural that Shining Armor got to know Cadance through his foalsat sister.
I have an idea of how they finally got together. I’m planning a little thing I hope to get (st)arted one day, showing the timeline from when Twilight was exiled to Ponyville, to before the Canterlot Wedding. That will take a lot of effort, but My Fair Cadance took a bit of effort too, so here’s hoping I can pull this off.
(Shameless plug) My Fair Cadance: DeviantArt | PayHip