There's nothing really simple that you're missing.
However, I don't know about Topaz but all the Nik filters can be launched from PS smart objects. Instead of getting a flattened TIF back, you get a TIF with your Nik work as a smart filter (a type of layer) so you can fine tune whatever you have done. You start from LR, Edit With Photoshop, right click the image layer and convert it to a smart object, then launch the Nik plugin. Afterwards, the layer has the Nik settings and you can just double click it to relaunch the Nik plugin and change whatever you want.