Right match

The M8 has a phono stage, according to the website, claiming for both MM and MC.  So along mesch's lines, (1) did you plug the TT into the phono input and (2) if so, did you plug it into the MM or MC input?  From your description it sounds like you might be using a lower output MC but going through the MM input.

Unless there is something not working properly in the preamp or amp, you'd have to assume that two Musical Fidelity products of the same product line should work fine together.  You might want to try the MM/MC switch to see if it makes an improvement (but keep the volume down to start).  It would probably help to know the make and model of your cartridge, and whether you're running balanced or RCA interconnects.  Have you tried the preamp with a CD player or other, non-turntable, source to see if the problem exists for that source?

Sounds like the problem is in the preamp, then, or maybe the connections.  I'd ask my dealer for help first before returning it.