Hi,
I found a solution here from another thread somewhere, or it may have been another site. I was adviced to use codes for "Philips". This will give you power, volume and mute controls. I tried all the Philips codes and the ones in the first line of them on your tivo menu work best. Some of the later ones work, but errors like volume down mute's the tv and such happened, but so far... I can use my new Syntax Olevia with my Series 2, and soon to be Humax DRT800.
Andy