Can I connect 2 Adcom Preamps?

Yes, just hook up the table to the GTP-500's phono input and use the preamp outputs to any line level input on your GTP-600. This will allow you to use the volume control on the GTP-500 to match levels, however a cleaner signal would be to use the tape outputs from the GTP-500 to any line level input on the GTP-600. If you do it this way, you will have a fixed output, but a cleaner signal path.

In addition to the response by Mofimadness, the GTP-500 has separate recording and listening selectors. If you use the preamp output, set the listening selector to phono, and if using the tape output, set the recording selector to phono.

Awesome thank you for the quick response. I am nowhere near home, but I will hook them up as soon as I get there. Thank you very much.

Ok just one more question I am almost done getting all this to work. I have connected all my speakers to my GFA-6000, but where do the inputs go to? I don't see anything on my GTP-600 that would accommodate them.

Preamp outputs from GTP-600 to inputs on GFA-6000.