In anki "Deck Options -> Advanced -> New interval -> 0.50" will make it so marking it as "Again" will cut the SRS interval by 50%, so i.e. if "easy" would have been "1 year", it now becomes "6 months" if it's easy the next time.
The above setting is called out in the "Adjust your New Interval" section of the link you provided, so it looks like you may have just missed that you already found the solution.
I've found 0.5 to be a good value, but you can tweak it of course. The default is 0, which gives the behavior you've observed (reset it all the way back).
> I think it would be awesome to pair SRS with high quality images and audio, which I find most helpful for language learning.
Anki cards can include images and audio, and while a little less well, they also support videos.
It's probably worth trying to create a deck within anki that does what you want before building your own system. It'll at least let you find actual issues with anki, rather than the surface-level misunderstandings of it you've got now.