I have a Yamaha RX620 receiver and I am trying to add a turntable. I bought a Teac 988, non amplified turntable and it did not work. Volume sounds hollow and distant. I returned it and got the Teac 688 amplified turntable and the volume is loud, but blurry. You cannot understand the voices. All that my Yamaha manual says is to use an MM cartridge or a high-output MC cartridge. The cartidge on the Teacs are VM. Could that be causing the problem. What is the difference between the MM and VM cartridges. What should I do.