Have you checked to see if you are using the MM setting on the pre and not the MC? The Moving Coil setting is for a low output cart. You need the MM setting (usually 47Kohm) which is a high gain output.
I found this online regarding the Audio Horizons TP 8 Phono Preamp..."Cartridge loading is accomplished by inserting special RCA plugs into designated jacks on the rear panel."
I found this online regarding the Audio Horizons TP 8 Phono Preamp..."Cartridge loading is accomplished by inserting special RCA plugs into designated jacks on the rear panel."