Which ports do I use to connect a Thorens TD166 turntable to a VSX D511 reciever, and does it require a pre - amp

According to the specs there aren't any phono inputs which would have their own preamp. Everything else is line level so I'm pretty sure you'll need a preamp either between the turntable and one of the line level inputs or built into the turntable.

You may need a phono pre-amp to connect it to your unit. Newer receivers do not have a phono input for the record player and require a phono pre-amp to amplify the sound before going into the unit.
http://www.guitarcenter.com/Behringer-Microphono-PP400-Phono-Preamp-104009048-i1125385.gc

Are you meaning it doesn't have a connection for a turntable, just aux connections etc?
Check if it has a magnetic cartridge pre-amp first, if it doesn't you can get one just put the words: magnetic cartridge pre-amp, into Google to find one. Once you get it that will plug into an aux socket and the turntable into that, so you can hear the sound.

use a PRE-AMP or connect it to the PHONO input of an amp.

You didnt sa what it was connected to ???

Try setting the speaker settings on the receiver to small.

I've got the same model and the pre out transistor needs to be replaced,
sometimes you can get it to work by unplugging the reciever and the pre out
then plug in the reciever and plug the pre out in a couple of times or so untill it comes on
or unplug the amp from the wall then plug in the pre out , turn on the reciever wait for sounds to come on then plug in the amp.
if that don't do it the pre out transistor needs to be replaced

sounds like you need a phono pre-amp

All you have to do is connect the coaxial out from pc to any audio i/p at the back of vsx d512.but ensure you select the right channel to play the audio ( eg. tape i/p select tape at front control, aux i/p select the aux at front control )

You need to connect most turntables to a PHONO input or buy a PHONO preamp. Many newer receivers do not have a PHONO input. The AUX port you are using would work fine for a device like a CD player, but turntables need to be amplified. You can buy an external Phono pre-amp from Radio Shack. I don't know anything about this site, but something like this device should work for you. http://www.phonopreamps.com/tc400pp.html