While aware that you can shoot over to Topaz Studio from within Photoshop, at that point you are simply editing a pixel based file, such as a tiff. What about starting with Topaz Studio and moving to Photoshop for pixel based editing and output? (The same way you start with ACR, for example.)
Right now the only way I can do it, unless I am missing something, is to save out the file, somewhere, then open it up in Photoshop.This is a kludge, taking time and resulting in more files, etc.
Topaz Studio is an interesting app (I own it) but so far what I see is a congregation of plug-ins, with little utility in the raw conversion process. Translated as: why not stick with the plug-ins after all?