As I suspected. I took another drive with a good installation of OS 9.2.2, but no Sonnet extension, and installed the 2.3.1 version of the Sonnet software. Installed the HDD as Master on ATA bus 0, and Bingo! A case in which the latest and greatest(?) was not the best-advised.

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(60x) 13DT + 3PB + PTPro; (G3) 7DT/MT; (G4) 3T + PB. System 8.1 to OS 10.5.8