Right match

What cartridge is on your turntable?

There is a switch on the back of M8 that toggles between MM and MC.
Like I said if you are using a turntable, make sure it plugged into the phono input on the back of M8, it is grounded to the ground screw, and the MM/MC toggle switch is set according to the type of cartridge you’re using. So tell us what cartridge it is. Or just try flipping the MM/MC switch to MC. Report back what you’re hearing. 

Also, your M8 output impedance is 47ohm and a perfect match with your amplifier’s input impedance of 50kohm.

Or plug an iPhone or iPad into and RCA adapter and see if that sounds good.
Just not on a phono input, use an Aux, or some other line level.

My TT is MM