If I run my turntable on "line" through the NAD I can definitely get it up loud enough. If I switch it to phono, it still comes through the speakers, but incredibly quiet.Setting the switch to "line" routes the signal from the cartridge through a built-in phono preamp, while setting it to "phono" will bypass that phono preamp, and output the signal straight from the cartridge. The "phono" position will be used with an external phono preamp.
I do agree with a TT upgrade, however the first step should be that external phono preamp, as this will be needed when using an upgraded TT.