I have disobeyed the "rules" and put them in heavy-ish soil (adobe that's been ammended with many things - compost, manure, etc.) and they thrive. The Spuria Iris Society recommendation is at the link below.

As to manure..............most plants love aged manure. I'm unsure what a manure mix is and what is your native soil like?.

I set bags of the cheapest manure aside for 3 months before using. You can tell if it's still 'hot' by laying your hand on the bag. Hot manure will kill new roots.

Here is a link that might be useful: http://www.spuriairis.com/culture.htm