Mmcoy, no linestage has 84db gain. You can't use the above formula for an integrated amp, unless the specs show a separate figure for the linestage section. Most linestages have between 12db and 20db gain. There are some a little higher and some a little lower, but most are typically in the 12-20db area.
28db gain in the phono section is a very low gain figure. You are limited to high output MM type cartridges with a phono stage like that. If you want a step up device that would get you into the real low output MC range, you'll need about a 30db step up unit. And even that could be a little marginal for some cartridges.
You set the impedance on the phono stage or the step up device. If the phono stage has no allowance for this, then you'll really need to use a step up, or maybe you might consider a high-gain outboard phono stage for that purpose, and just don't use the CJ phono stage.