re:
Post 24.
I was looking at the connector for the HS-Link output from a DP-720 according to the service manual circuit diagram, and the pins are as described in my post #23.
It's possible that HS-Link (2) uses all pins with higher transmission rates. Your diagram does not show any shielded connections.
In any case a standard type Ethernet cable can be used, since a straight connection is compatible. A shielded type is highly recommended still for those interested in buying other than the Accuphase AHDL-15 which model number remains unchanged, so presume they connected pins 4 & 5 in the cable but didn't use them on the devices prior to introduction of HS-Link 2.