Just bought a 40" Panasonic TX-40C300B TV and have tried both using a code search and device codes (including a few from Panasonic) but cannot get volume control to operate from the TiVo handset only the Panasonic one. Panasonic say this is the TiVo manufacturers problem. Any solution would be appreciated.
I'd like to welcome you to the forums and start by saying I'm really sorry to read that you've not been able to find a code to work on your new Panasonic TV.
As you've already done both the manual code search and the device codes, then it does look like that your TV is not currently supported. This is not to say that it will never work, as things do get update regularly, though I wouldn't want to even attempt to place a guess on when our TiVo® remote will be able to support your TV.
I'd have to advise at the moment to keep checking the manual search option from time to time, as it may well find a relevant code.