How much power goes to the speakers without the external amp and how does the ampless system compare? Subaru VDCs have the Mcintosh and all have an amplifier under the passenger seat. '01 - '02s have a head unit with single CD and cassette, and the '03 - '04s have a six disc changer with no cassette. While the 14 pin plug is the same as non-Mcintosh cars, power to all seven speakers comes from the amp. Check the wiring diagrams.
For what it is worth, a US head will work and interchange with the JDM head in a JDM system.