HI Lewm -
The TT should have a built in phono preamp (like the Audio Technics 120 and any number of other TT's).
The TT would be a line input to the powered speakers, so the power output of the amplifiers (most likely Class D) inside the speakers would determine how loud it would play.
Don't let the relative inexpensive price tag throw you. These powered speakers/ TT systems sound pretty decent for what they are.
Rich