Aside from RG174 being 50 ohms, it is fundamentally impossible to supply an installable RCA harness with shielded cable of any kind. The two conductors would prevent the two halves, center and shell, from separating as is necessary to get the connector installed in the back of the Empeg. By using two entirely separate conductors, it is easy to disassemble the harness. With an RG174 based harness, one would first have half of to unsolder the cable from the RCA jack or would have to receive an unassembled assembly from the start. I suspect either avenue would displease a few folks.

Stu