I expect you are asking how to connect Accuphase DG-68 Voicing Equalizer.
Your list of equipment allows you to use different speaker connection schemes. Without a block diagram, it is difficult to answer precisely, but the principle of connecting the DG-68 does not change – the device must be connected into a low signal line.
I’d like to recommend to use digital connection DG-68 in a line between CD player DP-750 and C-2850 preamplifier as indicated in manufacturer documentation: 
Then the signal from C-2850 output is fed in the same way as you do without using DG-68.
If you like to use analog connection, then you can use XLR or RCA cables to attach DG-68 voicing equalizer between CD player and preamp:
Or between preamp output and power amps as shown in such a diagram:
In this situation, the connection of your power amplifiers also remains as it was without the use of DG-68.
If the answer does not suit you, please describe in more detail your intention for using P-7300 and A-75 power amps.