My first post gets deleted due to linking to a site that belongs to a banned member. I had no idea, not a good start getting your first post deleted !
I'll try again...
I have read that headphones shouldn't be less than eight times the output impedance of the amplifiers phone jack.
I have two older sansui amps (AU-4400 & AU-317) which I believe have an output impedance of around 8 ohms, its hard to actually find the specs to confirm this. The headphones I use are Denon AH-D2000's and AH-D5000's which have 25 ohm impendance at 1 kHz.
Does this rule still apply with modern headphones ? Would I be better off going for high impedance headphones for use with these amps ?