I don't think there would be enough 'differece' between the Galaxy and the Audax to make it a good choice for a second bike. I would leave consideration of that until your portfolio 'needs' a winter training or pure Audax machine. A pure road bike will give you the greatest benefit and be the biggest contrast to what you already have. The good news is that cheaper, aluminium frames work really well in big sizes for big blokes. What in a smaller size may be over 'harsh' often scales up to be 'taut and responsive' in the larger sizes. In the recent C+ they rated the Boardman bike from Halfords to be excellent at that sort of price point.