There is at least one other seller on eBay selling an 8 pin cable for the FTDX-10 to connect to a linear.
That listing explains that it is an 8 pin amp connector for the tuner connector.
Page 13 of the FTDX-10 Op manual shows that the Tuner connector has the same TX-Gnd signal that the Linear connector has and, of course, ground. Those are two signals needed for a basic RCA connection to key a linear amp. They "seem" to be the same signals as on the Linear connector, but that needs to be verified.
I think he could have put a clear explanation on the posting. I've dealt with RadioDan in the past, and there were no issues.
In my opinion, Yaesu caused problems by not including a mating 10 pin miniDIN connector with the radio. It's not that easy to find one.
One thing I'm not sure of--will the same delay menu settings apply to the signals on the Tuner Connector as on the Linear Connector.
Suggest verifying on the schematic that the signals are the same on both connectors, or ask Dan. I would check, but I no longer have my FTDX-10.
GL,
John, KB1NO