I have a 6-in-1 upgradeable URC-4300, and would love some help in upgrading it. Any takers? Here are the details...

It's several years old and I'm trying to get it to work a couple of new devices (it's still works fine for my old ones). Thanks to the great list of codes on the web I think I've found the device codes I need, but my remote won't accept them (ie. it doesn't double blink after I enter them). So I'm sure I need to upgrade my remote to contain these codes. This is where my problem starts.

I've tried downloading the sound files from the 1-for-all web site (my manual says the URC-4300 is phone upgradeable). But I can't get my remote to communicate. I press Magic for 2 seconds and then power and the LED comes on - so it's ready to receive, but the sound file has no effect on it. The LED doesn't blink (while the sounds are playing or after) and stays on for 30 seconds after the sound file has finished. I've tried different volumes, different speakers, different computers, different positions of the remote and downloading the file again (several times) - but always the same result.
I've also tried downloading different codes, including ones I already use. And reinitialising the remote (with both 9-8-0 and 9-8-1). But the remote never accepts the sound files.

I've also tried the phone support. I'm in Australia and TEAC Sales now provides the support. They've told me that my model is no longer compatible with their hardware and I need to buy a new remote (this sounds a bit fishy to me).
And the 1-for-all help email is, well ..., unresponsive.

The URC-4300 has 3 holes in the battery compartment, so I don't have the luxury of being able to upgrade it with JP1.

That's my life story - Has anyone had similar upgrade problems? Any offers of advice?