I agree with dasilvarsa. There is no reason why the correct TTS voice won't work so downgrading the fw version would seem pointless. You may need to flash ID fw to use the voice.

I believe this is the correct file, but it also gives 'Incompatible Audio Version' in my US 1450:
Code:
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To flash it drag it onto updater.exe with your nuvi connected in preboot, or drag it on to WebUpdater with it connected in Mass Storage Mode. If it still won't flash, try the following:

To obtain the voice file, open Voice,Indonesian,Damayanti_TTS__WebUpdater__100.rgn with [Only registered and activated users can see links. ], you will receive a message 'unsupported section identifier: XXXX', press "OK" to continue. Then use the 'Save' button to save 'unknown.bin' and change it's name and extension to 'Indonesian__Damayanti.vpm'. The file size should be 21,402 KB and the MD5 hash is DAC1C19B09ACE27105BD169FC9D2E626. Put the voice file with that exact name in your nuvi's Voice folder removing any other version of the voice.

I asked earlier "What is your device origin?" for a reason. So if the above doesn't work, can you confirm that you have an original US/EU hardware version or is it some other localised version 14x0 you have flashed to US/EU fw? It is possible to flash ID fw to other localisation hardware units provided the [Only registered and activated users can see links. ] are the same. ID 1460 has the same PCB P/N as US/EU 14x0.