And, typically, while it works in the VM it turns out that the FX5620 isn't supported by FreeBSD's implementation of ACPI:
ath_hal: 0.9.17.2 (AR5210, AR5211, AR5212, RF5111, RF5112, RF2413, RF5413)
ACPI-0159: *** Error: AcpiLoadTables: Could not get RSDP, AE_NO_ACPI_TABLES
ACPI-0213: *** Error: AcpiLoadTables: Could not load tables: AE_NO_ACPI_TABLES
ACPI: table load failed: AE_NO_ACPI_TABLES
Ah well, it was worth a go - I guess it'll just have to stay toasty :)