I've had this happen on at least one other installation. This is with a fresh minimal Stretch installation followed by installing 14.0.5 tdm-trinity and tdebase-trinity. When I boot multi-user.target, aplay works. Then I startx into TDE, an error sound briefly occurs, followed by the nosound indication from kmix, and no more sounds. I log off TDE, and aplay no longer works, until I do alsactl init again, after which aplay works only until another TDE session is started. Any ideas what's going on that TDE kills sound?

Attached are listed some installed packages plus snd modules: