If you want a multi-class Kensai-Diviner, you will have to start out either as a Fighter-Mage or as a Diviner.
When you start as a Fighter-Mage, you will have to open SK, and change the kit (not the class!) to Diviner. That way you have a Fighter-Diviner. Then you want to add the affects -which I mentioned in my previous post- to the affects tab, so you will have a Kensai-Diviner multiclass. Remember to set the levels and experience back to zero if you want to have those extra spell slots.
When you start out as a Diviner, you change the class (not the kit!!) to Fighter-Mage. Add those Kensai bonuses ad set experience and levels back to zero. Personally, I think this is the safest route if you want those extra spell slots.
If somehow you are unable to get those extra spells, you might want to ask UserUnfriendly here, or pm him, since he knows how to add extra spells to a spell level. Me, I've never been interested in adding extra spells (only decreasing them

) and thus never asked UU or experimented with it.