Volume differs a lot for different inputs?

Phono level and line level will always have a difference in volume settings.

One is a low level input and one is a high level input.

Do you have a dedicated "phono" input on the unit you are using?

Also, this has nothing to do with the Technics being a "DJ" device.

Mofi is correct. The maximum output from a phono cartridge is typically between 0.25 and 5 millivolts. The max output from a CD player is typically around 1-2 volts, or roughly 1000X higher. In addition, the frequency response of an LP is modified for several technical reasons by something called the RIAA equalization curve. To get the proper tonal balance from an LP, a phono stage or phono pre-amp has a reverse RIAA equalization circuit. So it sounds like you need a phono stage aka phono pre-amp, or an amp or receiver that has one built in.