You've got a great summmary of the issue already posted. Passive vs active is an issue, the occasional tube amp will have an input selector with room for 2 or 3 sources. Some disc players have a higher output to start than others. I've got a modified player on which the mod knocked the output down quite a bit which wouldn't work well at all with a passive pre. This would be a time when I might look a little harder at reviews than I would otherwise. And if you see a "but it really opened up when in put my active brand X preamp in front of the amp" you'll know to move on.
Regards,
Larry R
Seattle
Regards,
Larry R
Seattle