Headphones may be the worst type of load for testing the LINE output characteristic of a 'Phones' jack on these recorders.
Headphones present a LOW/COMPLEX loading of the output amplifier, while LINE loading is anything but low impedance, and varies with the patch cable length, cable characteristic, and the input loading of a LINE level input that's rarely adding anything complex to cause signal degradation or loading difficulty.
That's the reason there are so many headphones amps on the market, and your favorite phones will sound differently with each device it's driven by, so don't be judging the sound quality of a LINE function with what you might hear on connected headphones.
It just may be the R-09HR does not have such a great low and complex load driving ability, or nearly as good as the older R-09 deck, but likely have excellent quality with LINE cable driving purposes.
Suggest holding off conclusions unless this is carefully tested with phones/line output jack connected to suitable phones or speaker amplifier for judging how this output works for simple less demanding line cable driving purposes.