KAB RF-1 subsonic filter

Yes, exactly. If you have a separate phono stage put it between the phono stage and preamp. The KAB then will have a consistent input and it will be less likely to be overdriven into distortion. You could also place it in a tape loop if you have one. 

The reason you want to do this is, whatever noise the filter makes will be attenuated along with the signal if the filter comes before the volume control. But after the volume control, the signal will be attenuated but not the noise! The signal to noise ratio will decrease along with the volume.

KAB recommend install the RF-1 between the phono stage and preamp

I've tried the filter installed here as well as between the preamp and main amp (which is where it currently is), no difference I have been able to discern with vinyl and digital sources sound no different as well. 

That said, just to appease my OCD, I likely will put it back in the phono to pre line as to not have one more variable in the line with other sources.