I assume that your voltmeter was set to read a AC signal and not a DC signal right?
If so, then the RCA outputs on the Empeg should be reading about .7 volt in AC mode.

If thats the same level that your tape deck in your mini-stereo outputs, then you're pretty safe to assume that the RCA outputs can connect to the signal INPUTS to your Amplifier in your mini-stereo.
Just keep your RCA wires and empeg well clear of the 10V wire - that could do some damage to your empeg if it got shorted onto the RCA cables by mistake.

The wire labelled AG is the "analogue ground" and is what the RCA cable (between your Amp in your mini stereo and the rear of the mini stereo) "shields" or outer wires in the cable should be wired to - and what one lead on your multimeter should be connected to - the other wire you conenct your multimeter to is the Left or Right "out" signal from the tape deck.
Don't know what the PG wire is for - some kind of Ground signal I'd bet.

The RCA cable to your rear RCA sockets in your mini-stereo will have the two "ground"/shield - (normally bare copper sheath or strands of wire) wires in the RCA cables joined together at the AG wire/connector.

The centre conductor in the each RCA "cable" will connect to the Left or right "input" wire to the mini-stereo as appropriate (red wire in RCA cable to right, white wire to left input) - this wire is normally sheathed from the outer shield/straded wire by a coloured sheath and this is the "signal" carrying conductor (the bare wire is the "ground" or return wire - more or less to simplify things).

Red RCA connector colours mean right channel - White RCA connector colours means this is the left/mono channel.

Look on the rear of your empeg, the two RCA outputs have Red or White "coloured rings" inside the RCA connector sockets to show left or right channel.


Other than the above, it sounds reasonable (- as all ideas do - at least until something goes wrong)