Any issue with doing this?

I want to run the audio from my TV thru my audio system, but I use a passive preamp because my balanced Theta D/A has a high enough gain to drive my amp for cd source material. The gain from the tv thru the passive is not sufficient for the volume that I want. Can I buy a seperate el-chepo line stage preamp and run the audio from my tv thru the active preamp to give is some gain ( play with the volume position and then leave it preset to a defined position that gives me the required volume) and then run the output from the active preamp back thru the passive so I can use the passive as a master volume control.
Yes, that should work, assuming the line stage preamp provides sufficient gain (which I think most would).

The only other concern which occurs to me is that sometimes hooking a tv system into an audio system, especially if the tv is fed via cable, can lead to ground loop/hum problems. But if that occurs, you should be able to resolve it via some combination of an in-line ground isolator for the cable, rearranging your ac connections, cheater plugs, etc. And perhaps your results going directly into the passive preamp are already indicative that you won't have that kind of problem.

-- Al