Nero Burning ROM

I am using Nero, latest version 6.61, I believe. When I copy a DVD at the default highest speed of 12x (16,020 kb/s), the copies play on my home DVD player, but not on my portable Kawasaki DVD player. If I slow the burning selection to 8x (11,080 kb/s), the copies play on both units. 2 questions:
1. Curious why this is true?
2. More importantly, is there a way to tell Nero to always go with the 8x selection when copying DVD's? (This way I won't forget to go with this speed.) I tried the Control Drive's Speed option, selecting 8x, but the default always goes back to 12x when I go to burn DVD. Interestingly, this Control Drive Speed also has a faster 16x speed that doesn't show up on the choices on the window where you burn the discs.

 

The easiest way with Nero to control the speed is usually to use a DVD disc which will only burn at a lower speed ie a DVD that is only certified to burn at 8x rather than the current "standard" of 12x.