2 - Most all encoders use a low pass filter around 15-16 kHz...effectively chopping off the highs. Lame is the one exception that allows you to turn this off using the -k option to get full bandwidth. At this time, however, I'm unsure of the complete effects of this manuever. Don't know if it slows down the encoding or adds artifacts. I've been using it though...and crossing my fingers..

I'd be pretty wary of eliminating the low pass filter. There's a reason it's in there. Those who are writing the encoder feel that it needs to be filtered else the artifacts will be too severe. You've got to believe that they know what they're doing. In the case of LAME, the filter is not fixed at 16 KHz but is variable depending on the bitrate. See this bit from the r3mix site.

http://users.belgacom.net/gc247244/critique.htm#PERFECT

-Dylan